I was looking over a map of where the Nazis invaded and they never attacked Sweden.
I was wondering why since it seems like a much better strategic move than invading Russia. Why might they have chosen not to do so?
Sweden was a vital source of iron ores to Germany, an important strategic resource for her war effort. Because the allies controlled the seas, Scandinavia was Germany's main source of good quality iron. Attacking Sweden would have disrupted the supply for no real gain.
Production of high-grade steel suitable for armour plate and gun barrels depended largely on the Bessemer process which, in turn, required ores of high phosphorus content. This Swedish iron had in plenty, and German foundries relied especially on supplies mined from ... northern Sweden.
Swedish ore was so essential to the German armaments industry, in fact, that as late as 1944, when the Reich's inland transportation network was under considerable strain, Germany went to great lengths to sustain its coal exports to Sweden in order to complete the exchange for ore.
- Greenhous, Brereton, et al. The Crucible of War, 1939-1945. The Official History of the Royal Canadian Air Force, Volume III. Toronto: Toronto University Press, 1994.
Politically, this also meant that Sweden, while neutral, continued to trade with Nazi Germany. Hitler could get what he needed from Sweden by diplomacy or coercion. Soviet Russia, in contrast, was an ideological enemy and a competing or potentially competing great power. Although it ended badly, that gave Hitler an actual motivation to invade (in addition to his personal issues).
Now, if Sweden refused to supply Germany's resource needs, then that would probably have increased the likelihood of an invasion; but Swedish leaders cooperated with Hitler.
For the same reason he did not invade Switzerland, the cost-benefit ratio was not good.
Also, you should realize that the Germans were not just a bunch of frenzied madmen attacking everybody. They were happy to co-exist with other countries that were friendly, such as Sweden. After the war started, many countries, including the United States (1941), Britain (1939) and France (1939), cut off commercial ties with Germany, which meant that Germany could not trade or do banking in those countries. Sweden, Switzerland, Spain and Portugal did not cut off trade and did business with Germany normally. As far as Germany was concerned why would they want to attack them? They were friends. It's kind of like saying, hey, the United States could easily conquer Mexico and Canada, why aren't we doing it? Germany primarily attacked countries that were either outright enemies, or were expected to become enemies in the near future.
Comment on Business Relations with the US/Americas
Some people in the comments seem to have taken exception to my comment about Germany's loss of business with the US and other countries. I know there is sort of a propaganda cult about how American big business "conspired" with Nazi Germany, but the reality is that Germany and Italy's trade with the entire world other than Europe was curtailed by the British blockade which included wheat and coffee as "contraband". In fact, even a United States mail ship going to Italy was embargoed by the British on some pretext. The British not only stopped any ships from going to Germany, but often stole their cargo as well. All over the world German merchant ships tried to hide in neutral ports to no avail as Britain and the United States found any means to coerce the country involved to hand the ship over to them.
If the British blockade was not sufficient, changes to the Neutrality Act in 1939 gave Roosevelt the power to declare war zones and make it illegal for American citizens and ships to enter those zones. By declaring all of the Axis-controlled places "war zones" Roosevelt accomplished a de facto blockade of Germany even though the US was technically "neutral".
Possibly even more damaging to Germany business-wise, was not the economic blockade, but the financial blockade. The US, Britain and France all made their currency inconvertible to Deutschmarks as early as 1936. Since the Germans could not buy Dollars from the US Treasury, for example, and it was illegal under the neutrality acts for American banks to issue credit to any German company, this made it virtually impossible for Germany to buy US goods. A US manufacturer will not take Deutschmarks in payments, only dollars, so by cutting off the dollar supply to Germany, trade became not only extremely difficult not only with the United States, but even with their allies. For example, just to trade with Turkey was very awkward and required all kinds of wierd barter arrangements, even though Turkey was completely out of the Allied sphere of influence.
In 1941 when war was declared all vestigial business that the US was doing with Germany through third parties was ended.
It is somewhat important to realize that even Hitler was not so mad as to actually consider invading all of Europe, and getting away with it. He had to consider cost vs. benefit.
Hitler's target -- "the plan", as early as 1925 -- was the Soviet Union. That's where his ideological enemy was: Bolshevism. That's where his whole screwed "Lebensraum" vision played out: land, slaves, and resources.
As such, the pre-war invasions and occupations -- Austria, Sudetenland, Czechoslovakia -- and the attack on Poland were merely setting the stage for the attack on Soviet Russia.
But when England and France started switching from a policy of Appeasement to eventually declaring war on Germany after the invasion of Poland, he had to consider stabilizing his position to the west as well. That is where the second set of invasions and occupations comes in.
Denmark and Norway (crippling the German navy), to deny the northern flank to England, secure the Swedish iron ore supplies, and give the German navy some wiggle room in the North Sea. France (via the Netherlands, Belgium, and Luxembourg), the most direct threat to Germany and its industrial heart, the Ruhr area.
That last one succeeded beyond expectations, and rather surprisingly to everyone (including the Germans) an invasion of Britain itself was considered... Although you could say that Operation Sea Lion was (at least) as much an attempt to scare Britain into an armistice as a credible threat. At the same time Hitler was still deluded enough to make peace offers to Britain... which would have allowed him to focus all his powers on the Soviets.
So now he had to fortify France, fought the Battle of Britain (crippling the Luftwaffe), and had to help his ally Italy in North Africa, and handle the situation on the Balkans -- to deny England access and secure the supply of Romanian oil.
All this was a severe strain on available forces, and crucially delayed the attack on Soviet Russia. Had he been given the choice, he'd rather have done without all this.
Note that the first set of invasions was mostly offensive in nature: Getting at Russia. The second set was mostly defensive in nature ("defensive" in a very lose definition of the word): Securing his back, flanks, and access to crucial resources.
The second set was not originally part of "the plan". The historian in me is wondering what would have happened if France and Britain hadn't declared war, or if Britain had folded after the fall of France...
Now, Sweden... With Norway held by Germany, and Finland still free, Sweden was not under threat. It was much easier delivering coal to Sweden in exchange for ore than stretching the German war machine yet further and invade (probably disrupting the supply of ore for several months).
There was nothing to be gained from invading Sweden, and the German forces did not have the resources to spare anyway.
Sweden like Switzerland was a neutral country and not involved in the conflict. Attacking Sweden would have tied up military resources and it wasn't really necessary since the resources Germany needed from Sweden could be obtained by trade or diplomacy. See Wikipedia's article on Sweden during World War II for more information.
There was also an ideological base for it. Hitler thought the Swedes were good Aryans so the Nazis expected Sweden to become an ally after the war.
If we turn the question around. What benefits would an invasion give? Norway was occupied to prevent the allies from doing it (Plan R 4). The allied plans to occupy Sweden was cancelled so that reason disappeared.
It was because there was no STRATEGIC reason for Hitler to attack Sweden. Hitler goal is to colonize Slavic lands in eastern Europe, especially Poland and Russia. He attacked Norway to keep the Allies from opening a second font in the north. He attacked Belgium because it was on the way to France. He attacked France because France didn't want let him attack the east, which was always Hitler's goal. Sweden was already surrounded by Germany's friends and wasn't posing any threat, so there was no reason to attack. Yes Hitler was a genocidal maniac but even then, he wasn't trying to conquer all of Europe. He didn't officially annex most of France either, mainly just Alsace-Lorraine and I think some other parts near the border.
Why would it seem like a much better strategic move than invading Russia? They are extremely different propositions, it seems to me.
It proved true that Sweden did not need to be invaded. It continued to supply trade and needed resources (mainly iron), and not invading it had advantages such as having a neutral country nearby, which is useful for other sorts of trade and politics. Also, invading and occupying a country requires time and many resources, and can have various negative results, both immediately and indirectly.
From a purely military perspective, since France and England declared war on Germany when they attacked Poland, Germany decided to address that threat as quickly as possible, which they felt required securing Denmark and Norway first, to avoid being outflanked by a naval invasion while they moved against France. (Hitler had hoped France and England would remain neutral even as he went on to attack Russia; Russia was the opponent he was always most concerned with.)
The schedule of attacking Denmark and Norway was something that had to be done quickly in order to have time to redeploy for a crushing attack on France and the Low Countries (and Britain) as early as possible in 1940. Attacking Sweden after Norway would have been even more effort than Norway, and probably would have delayed and weakened the attack on France, for little or no immediate gain or even reason. The reason for attacking Denmark and Norway was to be able to defend the coast against invasion, while Sweden offers no invadable coast if Denmark and Norway are held.
Once France had fallen, again there was little reason to attack Sweden, but there was a similar rush to consolidate eastern European countries before moving on Russia in 1941. A common criticism of what Germany did was their effort to help Italy in Africa, which delayed the invasion of Russia. Invading Sweden would have similarly tied up forces and further delayed the invasion of Russia, but again would have had little or no reason and negative results, as well.
Even if there was seen to be a reason to attack Sweden, it would have been greatly outweighed by the competing military need to hit France and Russia as soon and as strongly as possible, to prevent them from building up defensive positions or going on the offensive themselves.
This situation has been clear in all of the World War II strategic wargame representations I have played, such as Third Reich, Hitler's War, or even the simplistic Strategic Command, all of which do let you invade Sweden for an advantage to production, but also in all of them, it's almost certain that doing so will mess up your ability to deploy quickly in strength against France and/or Russia, which is pretty clearly more important.
In some games, invading Sweden also tends to make it more likely that the United States will declare war on Germany (and start war mobilization) earlier, which is of course also a very bad thing.
As for why Sweden vs. Russia, Hitler and Stalin both anticipated eventual war with each other, and Sweden had no plan to fight Germany, and massively fewer resources with which to do it. The only way that choice makes sense to me is if you could find a way be sure to never have to fight Russia at all, which would have been better, but probably wouldn't involve attacking Sweden to achieve it (though it might involve letting Stalin invade Finland). That would require a very different mindset than actually existed, particularly while Hitler and Stalin continued to rule.
Sweden cooperated with Germany in World War II. (Although the Allies did manage to "launch" Eric Ericcson, a Swedish-American spy, from Sweden, in large part because Germans felt that Sweden was a potential "safe haven" for German "flight capital" by high-ranking Nazis.) My Swedish friends tell me that Sweden allowed Germany overflights to Norway during the Norwegian invasion. And they said, "The Norwegians never forgave us for that." As mentioned by others above, Sweden was a source of iron ore for Germany.
By June, 1940, Sweden was surrounded to the north and west by occupied Norway and Denmark, to the south by Germany itself, and to the east by pro-German Finland. Given Sweden's cooperation, there was no need to invade it to neutralize it. As is the case of Spain, Germany would much rather have a friendly neutral than an outright enemy.
Sweden was neutral while doing business with Germany, exactly the same as Switzerland. Sweden and Switzerland were basically allies of Germany with the good sense not to join a losing fight. In Europe's many previous 'great wars' Sweden always aligned with Germany.
Britain on the other hand started 2 world wars it couldn't win with the hope that America would bail them out.