Disclaimer: I understand this is a generalized statement and doesn't account for every scenario (for example: the US civil war).
In general, why, over the course of our whole history, have the United States and Canada had stable governments and rich economies, and South American countries have dealt with a lower standard of living, coups, cartels, failed governments, and poorer economic conditions and infrastructure?
T.E.D.'s answer is very good, and points to the most important issue: the difference between colonisation methods in North America vs Latin America. There are a few missing nexus that I feel could be explored in more depth, though.
But, first, as this is a question with very important political and ideological consequences, I also think it is necessary to dispell some (first-world-o-centric) fantasies about it, because those fantasies are widespread and noxious. So I will adress first what are not the causes of the differences between what went on North and South of Rio Grande, and only then proceed to a more encompassing explanation of the divide, which should show the actual place, if any, of the fantastic factors in the real order of things.
There is a strong tendency to anachronically read modern contents into mediaeval forms. One such misreading is that of the role and meaning of mediaeval parliaments. Those were not democratic institutions, and were probably instruments of feudal reaction rather than of democratic progress. Some comments pointed to the fact that the Spanish Cortes were older than English Parliament; this fact - and its omission by those proposing a difference between a supposedly democratic mediaeval England and a despotic Spain - shows that this was not an actual factor; if there were differences in the internal workings of England, compared to Spain, they must rely elsewhere, not in the existence of a parliament - at least, not in the existence of a parliament as an early step in the path to democracy.
But the Cortes predating Parliament are far from being the only evidence that democracy in metropoles had little to do with the difference in prosperity and political stability North or South of Rio Grande. Absolutism was only toppled in England by the Civil war and the two 17th century revolutions. But it was toppled earlier in two other places in Europe, namely Switzerland and Netherlands. And while Switzerland, being landlocked, had not its own colonial enterprises, the Netherlands were quite a major player in the colonial game. And albeit being socially much more similar to England than to Spain (and arguably even more far apart from Spain), Dutch colonisation mostly resulted in hellholes similar if not even worse than Spanish or Portuguese colonies. Plus we can see that the same metropolis delivered very different results, if we compare New England to Jamaica (or even to Georgia), Quebec to Haiti, or Peru to Uruguay or Costa Rica.
And, last but not least, we must at least suspect that the early development of democracy, industry, and capitalism in England, as compared with Spain, may very well not be an independent variable. Was the belated development of democracy in Spain and Portugal a cause of the lack of prosperity of their American colonies, or is it, the other way round, a consequence of their colonial enterprise?
Somewhat relatedly,
Other myth is that the work (and/or family) ethics of Protestantism (or more specifically Calvinism) would have resulted in more orderly and progressive societies than those that could be built under the hegemony of Catholicism. Again, the Netherlands are the counter-example that shows that this is not possible; while England was only very partially Calvinist (with a State Church that mixed elements of Catholicism and Calvinism, and a strong Catholic minority, the Netherlands were quite the Calvinist country, which didn't help Surinam or Java too much.
And, of course, albeit the many flaws of Catholicism, it is certainly not an ideology that promotes idleness or debauchery.
So, if work or family ethics have to do with differences between North and South (and I do think they do), such work or family ethics must be related to something else besides the religion of colonists.
Then we need address the apparent opposite of these social or political explanations. If not in the internal workings of European metropoles, could the key to the problem be in geographical factors?
Then there is the myth of the intractability of tropical climate, as put in a previous answer:
difficulty of colonizing areas in tropical/subtropical climates vs. colonizing temperate areas
That this is clearly not the case can be easily shown by the fact that Latin America was colonised a century before North America. Moreso, far from an inferno of tropical diseases, the whole "new world" was an epidemiological paradise. None of the main epidemic killers - malaria, smallpox, plague, cholera - were even known in the Americas: they were all brought from Europe, in which, the temperate climate of the area nonwhitstanding, they had been killing millions of people for hundreds of years. The plague alone, during its 1348 outburst, killed about one third to one half of the European population of the time. Those diseases may have originated in the tropics, and they certainly were eradicated later in the tropics than in temperate areas (where they were by the way defeated in the 19th century, by no means in the 16th), but to imagine that climate provides an effective barrier against their spread North of the Tropic of Cancer is false, and very contrary to historical evidence.
Plus, latitude is not the only factor in determining climate; altitude also counts and makes the climate of most of the western parts of Souther America, as well as Mexico, quite cool and even chilly - but neither Mexico nor the Andes correspond to any pockets of prosperity or political stability.
So climate played an important role in the differencen between North and South America, but not by making South America a hostile place for European colonists. The opposite, as will be argued below, is true.
Now we need to have a look at the internal workings of the colonies themselves, rather that those of the metropoles. The issue of slavery comes to mind.
One other possible explanation is the institution of slavery, which was overwhelming in Brazil and the Caribbean, and that must account for at least part of the differences between North and South America.
One problem with this is that slavery's geographical distribution doesn't really fit the divide between North and South. It was not present in the Andean region, which remains among the poorest subregions of Southern America, and was conspicuously present in English America's southernmost parts. That slavery does hamper prosperity and political stability is quite demonstrated by the fact that the regions of the United States where it was widespread remain the poorest parts of the country, and by the fact that the most important political upheaval in the independent United States was a Civil War intimately linked to the "peculiar institution". But in the absence of other factors, the dividing line between prosperity and misery would be different, and more similar to a meridian than to a parallel, separating Brazil, the Guyanas and the Caribbean, and American Old South from the western part of both South and North America.
So now we are prepared to give a more positive answer. Without necessarily ignoring the internal workings of the metropoles and their colonies, or geographical factors such as climate, we need to look at the specific relation between metropolis and colony, for there is the main difference, and the factor that can illuminate the aspects discussed above, and put them into their due place within the complex mechanism that generated two rich first world countries, one of them a global power, North of the Rio Grande, and a score of poor and very poor third world countries South of it.
That is, we must now take a look at what is called
The problem with any explanation that seeks to root the differences between Latin America and Anglo-America at the differences between England, on one hand, and Spain and Portugal, on the other, is that never mind how powerful and despotic the latter may have been, it was clearly physically impossible for them to exercise any kind of power over their American possessions directly from their metropolitan sieges. They needed rely on the loyalty of a layer of local merchants and landlords, and that layer would need to be allowed some latitude at making revenue from the colonies, so that the metropolis could profit either. That meant a great deal of local self-government, expressed in the cabildos and senados da câmara (which by they way constituted a direct continuation of the longstanding municipalist tradition in the Iberic peninsula - the absolutist monarchies of Portugal and Spain were never unstructured despotisms from above, but rooted firmly on the grounds of the landed aristocracy and the estamento mercantil).
This pact was the only way that the metropolis could exert real power in the colonies. But it rested on the possibility of extracting a great economic surplus in the Americas, and that possibility, in turn, was a function of the availability of commodities that were scarce or of difficult production in Europe. And those were to be either precious metals or tropical agricultural products.
Spain found that quickly, in the fabulous mines of Mexico and the Andes; Portugal had to build that by putting up a local agriculture and manufacture of sugar (in which it was followed by all Caribbean colonial powers, England, Netherlands, France, and Spain itself).
But either gold/silver/platinum mining or sugar (or cotton, tobacco, etc.) plantations demanded large properties, not small farms, and so the social structure of South and Central America, Mexico and the Caribbean - including the non-Iberic settlements - has been extremely inegalitarian from its start. This fitted well with the necessity of relying on a local social layer for political support for the respective Crowns. Huge properties were granted to loyalists and in turn granted their loyalty. This allowed Portugal and Spain to acquire immense wealth from their colonies, and this wealth in turn helped consolidate the power of their kings, the absolutism of their regimes, and the backwardness of their own social structure.
North America didn't offer England (or the Netherlands, or France) any similar possibilities. Precious metals were only discovered there in significant amounts after independence, and, being of temperate climate, the region couldn't, with the exception of the Old South, base an agriculture that produced goods that weren't easily produced in Europe itself. Animal extraction of fur was insufficient for a significant extraction of surplus, and unsustainable in the long run. And so North America was seen either as a direct territorial expansion of the mainland, or as place to send undesirables. And the "undesirables" of England or France were very different from the "undesirables" of Portugal or Spain. The latter never had significant presence of Protestantism, and expelled or forcibly converted their Jews before the colonial effort. But England and France were internally torn apart by religious dissidence, and America offered a exhaust valve for this problem. And this helps to put Reformation's role in the issue in perspective. It is not that the work or family ethics of protestantism was transported into North America, but that internal religious strife provided England and France with populations that were willing to try the luck in a new world - and also had "good" family and work ethics. In less religiously diverse Spain and Portugal, the population available for overseas adventures was much less family-oriented: marginalised populations, adventurers, "second sons" of the nobility. As a result, Portuguese and Spanish colonists didn't come here in families, but as individual lone males.
Similarly, this puts the "democracy" argument in its correct place. Late mediaeval/early modern England was not more "democratic" than Spain; but a displaced population of religious dissidents owning small farms and being basically egalitarian, with little social stratification, could, and probably needed, to build correspondingly democratic local self-government.
Conversely, while the English Parliament was not a democratic institution, it was a strong institution, that prevented England from developing a strong absolutism, comparable to that of Portugal, Spain, or France. This in turn made the English Crown much less able to control and subdue its American dependencies than Portugal or Spain. When, much later, under George III, England found the resolve to try and impose unto its American colonies rules similar to those that Portugal and Spain had been imposing to their dependencies, they were unable to do it, and instead provoked the independence of the whole region.
This puts also the slavery piece of the puzzle into its place: while the peculiar institution certainly acted as a strong brake to the development of societies it affected, its role was subordinate to the relation between metropolis and colony. Where the metropolis could impose a strict colonial pact, slavery imposed itself, as an easy expedient to muster huge numbers of workers subordinate to a small number of masters loyal to the crown. Where fore other reasons it was impossible to instate slavery, but the social structure was nonetheless extremely inequal - as in the Andes, where other forms of forced labour, more similar to serfdom, were the norm - its absence was not enough to avoid the underdevelopment of the region. Where slavery predominated but wasn't tied to a strict colonial pact, as in the Southern United States, its presence was insufficient to stop the development of a local ruling class relatively independent of the metropolitan centre. When later it became a hindrance to the capitalist development of the North, it was destroyed through war.
And so we can also deal with the role of climate. Far from obsting the colonisation of South America, its tropical climate made it easier, and more profitable, providing the relevant European powers with a foreign base to produce foreign goods, which could find excellent prices in Europe. It provided South and Central America with an economy that was complementary to Europe's.
That immediate prosperity, unfortunately, was not a boon, but a disgrace to the regions aflicted by it, because it originated a social layer of large proprietors, entrenched in privilege and willing to subordinate their countries to foreign rule as long as that rule preserved their privileges.
Conversely, where the temperate climate matched with a metropolis that could or needed get rid of significant numbers of population, colonies with a more democratic structure and more loose ties to the metropolitan centre developed. Where temperate climate didn't match this, as in Uruguay, Chile and Argentina, the local structures were similar to those in the tropical area, though much more sparsely populated (Uruguay is about the same size of the the Brazilian southernmost state of Rio Grande do Sul, and albeit an intensive drive on immigration to increase its population in the late 19th century, it still has a population corresponding to a third of that of Rio Grande do Sul). The apparent prosperity of Uruguay and Argentina in the early 19th century was correspondingly delusional, resting, as the economy of all of South America, on the export of primary products - in their case, meat.
In contrast, where the tropical climate, exceptionally, wasn't coupled with the rise of a colonial compradora elite, as in the case of Costa Rica, a less inequal and more stable society arised, and probably was unsuccesful at the development of a local independent capitalism due to its small size, rather than by climate or the other problems that plague Latin America.
Finally, no account of Latin America's problems is complete without referencing what axsvl77 exposes in his answer: active foreign intervention directly intended to hamper development. While this cannot be an original cause of lack of prosperity, since it evidently relies on the disparity in prosperity first place, it reinforces the problem - and is a direct and important cause of political instability, from the military interventions in Nicaragua, Cuba, Dominican Republic, to the more subdued and concealed support for internal coups as in Chile, Brazil, Paraguay, Argentina, Venezuela, etc. Such support for undemocratic forces by the most important democracy in the world isn't peculiar to Latin America, though: the same apparently irrational behaviour is repeated, in aggravated forms, in the Middle East. And it cannot be blamed on ignorance alone: where the United States were serious about helping their allies, as in Japan and South Korea, they knew better than relying on the military, the landed oligarchies, or the clergy, and instead pressed for land reforms, limitation of the military role in society, and secularism.
I don't believe the answer to this is known objectively. However, it may be worth looking at the different settlement histories of the two areas you are comparing.
Most of the American possessions, up until quite recently (19th century or so) were treated as resources to be tapped (or "looted" if you prefer) by the owning Europeans. This includes not just South and Central America, but most of the British Caribbean possessions, which were run largely as sugar plantations, and today aren't noticeably better off than their neighbors who used to be French or Spanish possessions. Their initial governments were formed and operated for hundreds of years much like giant corporations, with the intent to ensure that power was concentrated into the hands of the few people at the top (typically Europeans), and to ensure that nothing changed that might jeopardize their steady extraction of wealth.
Canada and the USA, on the other hand, were the sites of entire communities of Europeans transplanted across the ocean wholesale. These citizens demanded the rights and privileges they would have enjoyed back home, as much as was practical.
So it really isn't fair to compare the two. Not only did the former plantation subject economies get a later start on their freedom, but even after their masters were kicked out, they were still saddled with unfree societies.
It was pointed out in the comments (h/t to @Jeff), that this is essentially the argument made in Colonial Origins of Comparitive Development, an article by Daron Acemoglu, Simon Johnson, and James A. Robinson, that appeared in American Economic Review in 2001 (and available online through JSTOR, or here as a PDF).
A large factor in the advancement/financial disparity between the U.S./Canada and its neighbors to the south is the difficulty of colonizing areas in tropical/subtropical climates vs. colonizing temperate areas. The climates of these regions are vastly different. Very little of Earth's land lies in the temperate zone of the southern hemisphere.
(If I remember correctly this is somewhat covered in Jared Diamond's Guns, Germs, and Steel, but of course anyone playing Civilization or a Paradox history game such as Europa Universalis knows you stay away from the jungle.)
(From Reference.com: "Areas with temperate climate enjoy weather conditions without large temperature extremes and with rainfall occurring throughout the year.")
Before modern medicine (and even today), people living in warm or hot areas were more subject to disease (such as malaria, which continues to kill hundreds of thousands of people each year in tropical climates throughout the world), with livestock and the crops that have generally sustained civilization more subject to disease as well. Additionally, the grains and other crops such as wheat and potatoes that kept civilization going were grown in temperate climates and were less likely to die off due to extreme variations in weather.
For more on the crops that sustained settlers and where they were grown, see T.E.D.'s answer on another related question here. Note he refers to indigenous peoples being removed from temperate areas for farming land - one of the reasons you don't have large indigenous populations in temperate countries like the United States or Argentina, both of which received the largest influx of immigrants and both of which conquered and removed indigenous people. Note that Argentina has a larger GDP per capita than most Latin American countries, and has historically been somewhat more stable.
Combine this with the difficulty of taming the jungle vs. taming a temperate forest, and the ease of colonizing the United States vs. that of colonizing much of, for instance, Brazil becomes apparent.
Please see a simple map of the areas in temperate zones vs. the areas in tropical zones below, followed by a more complex climate map.
Below is the Koppen-Geiger map. T.E.D. posted a map similar to the one below in his answer that I linked above, stating that areas in green and tan are good for growing crops. In the case of this map below, which is slightly different, dark purple isn't terrible. Meanwhile, these areas are not as prone to disease.
Compare these to pretty much any GPD per capita map:
As Santiago wrote in a comment below, the area of Asia that lies in the temperate zone seems to be an anomaly between the first temperate/tropical zone map and the GDP map, but it is important to note that this area is sometimes called the "third pole of the world" for a reason (this is the reason I updated with the Koppen-Geiger map). While this area of Asia is in the temperate zone, the actual climate is cold and arid. Meanwhile, other anomalies between the Koppen-Geiger map and the GDP map lie in the middle east and Venezuela; oil explains the discrepancy.
First of all, note that the colonizing nations were all located in the temperate zone of the northern hemisphere, in areas that are green in the Koppen-Geiger map.
Secondly, note that many of the states in the United States with the lowest income are in the subtropical areas of the country (only Mississippi shows this on the GDP map, but it remains true for the much of the southeast). These states still have a high GDP per capita compared to the nations below the Tropic of Cancer. I currently live in Florida, which benefits from a robust tourist industry and isn't as bad off as where I'm from in Alabama, and I can tell you that not many people lived in Florida until the invention of air conditioning and modern medicine (and without either of those I wouldn't live here). There is little local history other than small settlements dotting the state. Note that even the hottest parts of Florida are above the Tropic of Cancer.
For another example, see that tiny part of Australia that lies in the temperate zone, and the borders closest to it? See how the green areas are all in or near this zone? Compare it with this map of population density:
Most Australians live in or near the edge of the temperate zone, in the green areas of the Koppen-Geiger map, and even those people were dragged there from England, which was exactly in the middle of the temperate zone and is as dark green as you can get. One might also compare Australia and New Zealand and their places in or near the temperate zone and their higher GPD per capita than their neighbors to the north.
Now take a look at Uruguay, Argentina, and Chile, all of which have a relatively high GDP per capita compared to the rest of Latin America. These are the only major parts of South America in or near the temperate zone, and are the only areas that are green or tan. They are relatively free of malaria risk, and their higher GDP per capita compared to other Latin American countries likely corresponds to their climate.
On a similar note, as I mentioned in the beginning of this post, Argentina's climate caused it to receive a vast number of immigrants in comparison with the rest of the world, largely displacing its indigenous peoples.
The strength of the immigration and its contribution to the Argentine ethnography is evident by observing that Argentina became the second country in the world that received the most immigrants, with 6.6 millions, second only to the United States with 27 millions, and ahead of countries such as Canada, Brazil, Australia, etc.
As for politics: the politics of places that have a higher GPD per capita and less strife between indigenous peoples and immigrants are generally better over the long term.
---EDIT---
Since another answer by Luís Henrique called my claims out specifically (all's fair, I have no issue with this), I will attempt to answer issues brought up in said answer. I hope my tone here is not seen as aggressive, though it will likely come off as argumentative to some. No offense to Luis or any others who disagree is intended.
- "difficulty of colonizing areas in tropical/subtropical climates vs. colonizing temperate areas" - That this is clearly not the case can be easily shown by the fact that Latin America was colonised a century before North America.
Latin America wasn't "colonized" a century before North America, it was conquered, largely with the help of armies of thousands of native renegades (not with 500 Spanish soldiers, etc. etc.). The vast wealth from said conquering fueled a continued surge in "colonization" efforts, which consisted of controlling people who already knew how to survive in their own land. Actual self-sufficient colonies of Europeans would only gain footholds in good climates, and even then only when technology was sufficiently advanced.
- far from an inferno of tropical diseases, the whole "new world" was an epidemiological paradise. None of the main epidemic killers - malaria, smallpox, plague, cholera - were even known in the Americas: they were all brought from Europe, in which, the temperate climate of the area nonwhitstanding, they had been killing millions of people for hundreds of years.
Regardless of whether they existed BEFORE colonization, they certainly existed DURING colonization. How they came to exist in the jungle is not at issue. Meanwhile, the constant presence of malaria was not much of an issue for most of Europe; pandemics sweeping through areas that had enough food to sustain large populations but not enough technology/information to be able to combat said pandemics were the main problem, and populations recovered rapidly given the abundance of arable land in said areas. There is no argument being made that disease was not an issue for colonists in temperate climates. The argument is that disease, especially cholera and malaria, was not nearly as devastating in these areas as it was in tropical climates. Disease - especially mosquito-borne disease - is simply more prevalent in hot areas where freezes do not regularly reduce insect populations. Just ask anybody in the southeast U.S. who has had to deal with rampant mosquito populations after a mild winter.
- Those diseases [...] were by the way defeated in the 19th century
Malaria remains a threat in some areas in Latin America, and it was certainly not defeated in the 19th century. Its origins were barely understood until the end of the 19th century, and the construction of the Panama Canal in the early 20th century nearly failed (due to nearly every worker coming down with malaria) before the powers attempting its construction figured out preventative measures. While quinine as a treatment for malaria was discovered prior to this, it is doubtless that the common poor had a hard time coming by it, as the trees that provided it grew solely in areas surrounding Peru and demand was worldwide.
- To imagine that climate provides an effective barrier against their spread North of the Tropic of Cancer is false, and very contrary to historical evidence.
Climate provided an effective barrier to malaria north of subtropical climes, not north of the Tropic of Cancer. It was, in fact, the leading killer of colonial women in the southeast United States in the 19th century. As I have said earlier in this post, the southeast United States is the poorest area of the nation, and hot/humid areas such as Florida did not receive large influxes of European settlers even after Florida was won from Spain. And in spite of the existence of malaria in subtropical climates, its larger prevalence in areas that are most hospitable to mosquitos - tropical climates - is obvious on its face.
- Latitude is not the only factor in determining climate; altitude also counts and makes the climate of most of the western parts of Souther America, as well as Mexico, quite cool and even chilly - but neither Mexico nor the Andes correspond to any pockets of prosperity or political stability.
As I have explained (when I brought up "the third pole of the world"), high, chilly, mountainous areas do not make for large populations of wealthy individuals. There is no argument being made that mountains make for better colonization than jungle.
- Far from obsting the colonisation of South America, its tropical climate made it easier, and more profitable, providing the relevant European powers with a foreign base to produce foreign goods, which could find excellent prices in Europe. It provided South and Central America with an economy that was complementary to Europe's.
Yes, extracting wealth from conquered colonies rich in exotic goods was profitable for the colonizing powers. Was it profitable for the average person living in the colonies? Was it profitable for the exploited natives or the slaves that had to be brought in when the natives died of disease? No, even you argue the opposite:
- That immediate prosperity, unfortunately, was not a boon, but a disgrace to the regions aflicted by it, because it originated a social layer of large proprietors, entrenched in privilege and willing to subordinate their countries to foreign rule as long as that rule preserved their privileges.
The U.S. and Canada were run by colonists (to a large extent) for colonists, and colonies had been founded exclusively by Europeans moving to an area that had a climate just like the climate they were leaving. Argentina was founded in much the same way, as I have argued. These countries drove out native peoples to found their self-sufficient colonies.
The neighbors to the south were run like companies, their sole purpose to extract value. The people were not driven out; they were the exploited workers. The peoples could not be powerful and self-sufficient given the technology and crop packages of the settlers there. This accounts for much of the disparity between the U.S. and Canada and their neighbors to the south, and is a direct result of the different climates and how the land could be used.
- Conversely, where the temperate climate matched with a metropolis that could or needed get rid of significant numbers of population, colonies with a more democratic structure and more loose ties to the metropolitan centre developed. Where temperate climate didn't match this, as in Uruguay, Chile and Argentina, the local structures were similar to those in the tropical area, though much more sparsely populated (Uruguay is about the same size of the the Brazilian southernmost state of Rio Grande do Sul, and albeit an intensive drive on immigration to increase its population in the late 19th century, it still has a population corresponding to a third of that of Rio Grande do Sul).
It’s hard to tell what is being said here, but these areas extended from subtropical to temperate, were better off, and as I said before Argentina received the 2nd most amount of immigrants of all European colonies. The part of Brazil in this area, Rio Grande do Sul, is 1.6 times the size of Uruguay, its larger population is centered around Porto Alegre, a port where five rivers converge and a chief industrial and commercial center of Brazil, and Uruguay’s GDP per capita and its GDP per capita are equitable.
- The apparent prosperity of Uruguay and Argentina in the early 19th century was correspondingly delusional, resting, as the economy of all of South America, on the export of primary products - in their case, meat.
So they could grow enough food to feed themselves, then enough grain or arable grassland to feed enough cattle that they could get rich off of exporting meat, and this is "delusional" prosperity? It sounds like regular prosperity to me, the type of prosperity that could only come from a place with regular rainfall and a climate hospitable to the European crop/livestock package. This is, in fact, the same kind of cattle-focused prosperity that led to the expansion of the U.S. into the western states. Meanwhile, once again, the GDP per capita in these places is still much higher to this day. That is not delusion.
- In contrast, where the tropical climate, exceptionally, wasn't coupled with the rise of a colonial compradora elite, as in the case of Costa Rica, a less inequal and more stable society arised, and probably was unsuccesful at the development of a local independent capitalism due to its small size, rather than by climate or the other problems that plague Latin America.
Tropical climes were coupled with the rise of colonial elites precisely because they were tropical climes in which value was extracted but in which immigrants from Europe did not want to live. Meanwhile, one might argue that Costa Rica's main problem developing local independent capitalism was that it was covered in jungle.
Of course there were many factors. But the Spanish/Portugal scheme was a rural patron/peon arrangement that had not reached the bourgeoisie stage, i.e. an educated third estate. The British and particularly the French thinking in this regard, laid the ground work for the American founders’ derivative political philosophy.
The American frontier also allowed for varying people such as the Scotch-Irish to coexist. When some of these degrees of freedom diminished, the United States also had growing pains such as the Civil War and an unfortunate colonial period (Spanish/American war}.
TED's answer is fantastic; it covers the root causes of the problems. I'd like to add one more cause, specifically, US military and economic intervention in Central and South America have acted to keep these countries poor. Edit: The new answer by Luís Henrique provides a ton of detail.
Some examples, working from South to North:
US administration of Cuba, Haiti, Dominican Republic
These are just a few examples of US intervention; most people from South America are well aware that the US has been meddling in their affairs for decades, generally to the benefit of the US and not to the common welfare of South American people.
The US generally backs rightist oligarchy/aristocracy types against popular rebellions, so honestly, we can't blame the US 100% for these problems; really the South/Central American ruling classes refusing to share power and wealth with the people is the primary cause.
However, without US help, it is unlikely that popular reform would have been as suppressed for as long.
There are undoubtedly many reasons, but one is that the institutions of democracy and capitalism require a long period of development before they become strong and healthy.
England had Magna Carta and a parliament starting in 1215. There was a longstanding tradition of militias, in which every adult male (sometimes subject to religious and property requirements) was expected to keep arms and know how to use them. There was a long and gradual struggle in which the monarchy was progressively weakened. The English colonists in the New World brought with them their ideas about representative government and the rights of Englishmen, and they had a hundred years of practice running their own colonial democracies before 1776.
Spain never even experimented with republican forms of government until 1874, and it didn't achieve a stable democracy until the late 20th century. Spanish colonists had never experienced democracy and didn't try to establish democracies in the New World.
So basically in terms of their democratic traditions, the English-derived countries had an 800 year head start over the Spanish ones.
It's sort of a similar situation when you talk about the development of capitalism and modern economic liberalism. Although we don't have specific dates when we can say that the industrial revolution happened in England, etc., they were clearly way ahead of Spain in that department.
The most important reasons go back to the differences between the English colonial heritage in North America, and the Spanish/Portuguese colonial heritage in South America.
Although England, Spain and Portugal were all monarchies during the colonial period, and even today, England had "Republican" and "Democratic" traditions going back for centuries. This started with the Magna Carta in 1215, and continued with the (English) Bill of Rights in 1689, that limited the power of the king, and gave power to elected legislators. These documents led to American Constitution and Bill of Rights. Basically, North American people were relatively content with the their governments because they felt that they were fairly represented.
There were no counterparts in Spanish history to these limitations on royal power, and the imposition of "popular" power through elections. This meant that English colonial rule was milder and less centralized than that of Spanish colonies, during the colonial period, which led to more democratic and less authoritarian societies in North America, even after the independence movements.
Another issue was that the Spanish colonies were established as money-generating (gold and silver) entities, almost from the get-go, which is to say that they were heavily taxed. On the other hand, British colonies were established largely to transfer malcontents from the British Isles to the New World, and were not seen as sources of tax revenue until the 1760s, which is to say that the English colonies had much more freedom to develop economically.
First, a clarification: North America includes many more sovereign states than just the USA and Canada.
As for why the USA and Canada have been more prosperous than other American sovereign states, territories, etc, there are many factors. My answer will just consider two factors: anti-competitive interventions, and political fragmentation. My answer is grossly incomplete and barely scratches the surface of your vast question, so please just take it as a starting point for further reading.
These have their roots in military power, starting with naval power and progressing to more clandestine expressions of power.
From before the Elizabethan period, right through to this century, various south and central American and Caribbean societies have been subjected to powerfully disruptive interventions. These included:
a colonisation perhaps even more brutal than that inflicted upon north Americans (see A Short Account of the Destruction of the Indies (Bartolomé de las Casas, 1552));
looting and other interference with Spanish colonies and shipping by Francis Drake and others;
the support of coups that established dictatorships and undermined democratic civil society in the region;
the imposition of legal and physical barriers to economic interaction.
By forming a federal government, the USA was able to reduce political fragmentation within its borders and to create a huge internal market with the same four freedoms of movement as were later adopted in the European Single Market:
This provided the USA with a reduced amount of internal military conflict (e.g. one civil war, compared to many international and civil wars), and an immense global economic advantage. This economic advantage helped empower the U.S.A. to pursue F.D.R.'s Four Freedoms, which are about as concise a definition of prosperity as one could ask for:
Canada's colonisation was less brutal than many colonisations. This, combined with long periods of military and economic protection under the British Empire and, later, in the Commonwealth of Nations, and also in conjunction with Canadian federalism, allowed for both of the above sets of four freedoms to broadly apply to Canadian residents, both within Canada and across the British Empire and, later the Commonwealth.
By comparison, the rest of the American territories have been, historically, more politically and economically fragmented. This means they have had smaller markets available to them, and they have faced greater military threats from other nations. Both these factors reduce the likelihood of achieving prosperity.
I think this discussion must involve Max Weber's The Protestant Ethic and the Spirit of Capitalism.
Weber argued that Protestantism induces a mindset in its followers which aligns well with and promotes secular endeavors. The protestant god is a bookkeeper: There is an eternal record continuously updated with your good and bad deeds, and when you die a balance (!) will be drawn. Being industrious and frugal is good for your balance. Being wasteful and lazy is bad. How well your record is doing can be deduced from how well you are doing. ("I must be doing something right, because I'm rich/president/C.E.O. and you are not.")
Oppose this with the catholic god which can give absolution when necessary and is altogether more friendly towards the good life.
There has been positive and negative criticism since its publication; counter-examples which come immediately to mind are that catholic France is economically very comparable to partly protestant Germany, and that the southern, catholic parts of Germany are now more prosperous than the northern, protestant parts.
On the other hand opposing North and South Europe or North and South America as Europe's spitting image seems to support the cliché of an industrious northern mindset and a less disciplined southern mindset.1 Weber's theory was that the alignment with religious borders is no coincidence.
1To avoid misunderstandings let me assure you that I feel personally closer to the latter.
My answer is a little more simplistic than most, but here goes. When people left Britain for the colonies, it was to escape religious persecution, mostly. You had people all sharing a common motivation to make it work. When the Spanish landed in South and Central America, it was to loot it for riches. Don't underestimate the power of a people with a common goal versus a smattering of people trying to just make something work. Many of the people in South/Central America were either just left behind or natives with a very diminished or destroyed leadership.
In North America, you had western Europeans who migrated, mostly by will, and were still propped up by the existing government.
Argentina was actually ranked one in the top 10 economies of the world in the late 1800ds.
Infrastructure engineering with torrential rain in the tropics is more difficult, and the jungle was endless, even through flood basins, so trans continental rail links only were completed in South America in 1912 from Atlantic to Pacific.
The human cost of tropical infectious disease is high. The mortality rate for whites near jungles was higher back then, with yellow fever and so forth, which meant that the indigenous people had less of an western exodus to fight against, and were less threatened. South america was not a perfect haven for western colonialists.
The North and Midwest constructed networks that linked every city by 1860. In the heavily settled Midwestern Corn Belt, over 80 percent of farms were within 5 miles (8 km) of a railway, facilitating the shipment of grain, hogs and cattle to national and international markets. Brazil by comparison built it's first rail line of 14 kilometers at that time.
England, France, Holland, Belgium were more technologically and industrially advanced after 1800, so the technological infrastructure of north america developed in tandem with the UK and France. entire european cities like NYC were just outposts of Europe, same culture as London or Paris, same technology and power, same climate. In north america,
The quality of the metalworking, machines, guns, engines, trains, cars of america was very high and the education and middle class litteracy of american settlers was similar to European ones.
Geography is a factor. The United States began as a collection of States that shared a common seaboard; communication across the states could happen quickly, which helped to build a sense of common solidarity and shared national identity that served to counter the Federalist momentum from the different states.
South American geography, with the variety of climates, Andes mountains, Amazon river basin, and lack of a shared coastline, does not lend itself to easy communications. The resultant delay in information flow actually encourages feelings of "otherness" and diminishes any shared identity of the various peoples, which results in a natural tendency towards distinct nation-states instead of a larger sense of shared collectivism.
The lack of industrialization due to the difficulty to mass produce in humid and less than ideal conditions caused South America to lag behind the north. South America relied on agriculture creating the "Banana Republic" paradigm as our less developed neighbors fell behind we subverted their political structures to suit our needs in the North.
We have also crafted South American economies through our demands of exports. Unlike with say China which we demanded cheaply produced items from. We demanded what was Unique from South American geography, tropical fruits, plants for medicines, and mass crops such as coffee and sugar when possible.
As said above, TED's answer was a good one, and JackArbiter was close on conclusion(that the climate is a factor), but way off on explanation in my opinion.
Early on, I would say that surviving the winter required colonists to work together. Colonists and later frontier farmers would spend the summer farming, and then hunker down for the winter and wait it out. If you ran out of potatoes, etc, you would ask a neighbor if they could spare some so you could make it through.
That food scaricity is mentioned here:
http://www.ncpedia.org/colonial-farming-and-food-famine
You needed help farming your fields, you needed help reaping so that a stray storm wouldn't ruin your harvest. All of this builds community, good will, and trust. You don't steal from someone who helped your family live through the winter.
As society became more stable and land owners grew to have indentured servants(and later slaves) that culture was already established. Which brings me to my second point.
An African friend of mine recently pointed out that one of his countries problems is that their (corrupt) government officials are always buying European. So the officials embezzle and then rather than spending that money in the local economy, they spend it internationally, thus harming the local economy. That same issue applies here. Spain dug up or collected gold and then shipped it to Europe. The Spanish's very simplified accountants book would look like:
paid mine overseers: -5 silver
paid sailors: -10 silver
paid guards: -5 silver
received: 1 entire boat of gold
Spain made: 1 boat load of gold
Central and south America made 5 silver
Where the very simplified English's accountants would look like:
paid sailors: -10 silver
bought slaves: -10 gold
sold slaves: +14 gold
bought rum: -14 gold
sold rum: +16 gold
bought cotton: -16 gold
sold cotton: +20 gold
England made: 10 gold
USA/Canada made: 16 gold (in my simplified example that assumes crops are basically free)
Here is a link that talks about the trade triangle http://abolition.e2bn.org/slavery_43.html
Additionally, and I haven't found general statistics on this, but I would suspect that in the USA and Canada the land owners lived and banked locally, while in the Caribbean and south America the business and land owners lived and banked primarily in Europe. James Drax, the owner of Barbados certainly seems to have: https://en.wikipedia.org/wiki/James_Drax
A final note on infrastructure, culture, wars, and stability:
Industrialized war and the manufacturing this encourages may certainly be a small contributing factor, but if you look at the wars throughout Africa verses the wars through Europe, there doesn't seem to be a really consistent trend. Germany and France both in the last 100 years have had several large wars (and defeats) and coups and their economy seems to be doing fairly well. According to https://en.wikipedia.org/wiki/List_of_coups_d%27%C3%A9tat_and_coup_attempts_by_country several central and south american countries have had fewer. Some of Africa has never been to war, some of Africa is always at war http://www.independent.co.uk/news/world/politics/world-peace-these-are-the-only-11-countries-in-the-world-that-are-actually-free-from-conflict-9669623.html and it doesn't seem to matter.
Infrastructure seems to matter eg railroads: (map of countries with railroads):
as does a good highway system http://www.mapsofworld.com/world-top-ten/longest-road-network.html though this combined fits nearly all, but not all countries. The final thing, culture, probably matters a lot, but it is to hard to separate out. Being protestant is compelling, but isn't strictly conclusive, - why is Russia and their Eastern Orthodox doing well? Or France and their Catholic? This fits better with the culture caused by winter.
My guess is that The Wars of Roses to some minimal extent taught English speaking elites the value of moderation and compromise.
Usury may be an another factor - English Protestants accepted usury 250 earlier.
It is the United States and one measure of how important that is economically is the Civil War that was fought to keep this situation.
Jefferson's patent system -- extend that to all the states, one system. No idea how IP is protected in South America but I bet it requires the filing of multiple patents.
Somehow attracting the best people from all over the World and having a society in which they can be integrated, becoming Americans by becoming citizens. One might say, the US discriminated against immigrants and it did but eventually all legal discrimination was eliminated.
WW2 -- What did South America do? I don't think they built tanks and ships and planes to supply The Allies and while US allies were getting pounded, the US was unscathed and emerged number 1 not just by a little but by a long shot.
