Can anyone give an actual scientific reason why native Americans all "died from smallpox". Thanks
What genocide of the Native Americans? In specific times and places there were genocides of specific Native American nations, tribes, and other groups. But the vast majority of the Native American population decline was due to natural causes, namely diseases.
Suppose that in each generation a group's population has more deaths than births so that the next generation is 0.9 times as large as the first one. Suppose that each generation is thirty years long. So the first generation is 1.0 units, the second generation is 0.9 units after 30 years, the third generation is 0.81 units after sixty years, the fourth generation is 0.729 units after 90 years, the fifth generation is 0.6561 units after 120 years, the sixth generation is 0.59049 units after 150 years, the seventh generation is 0.531441 units after 180 years, the eighth generation is 0.4782969 units after 210 years, and so on.
So if a certain group had a population of 10,000 in 1600 and 4,782 in 1810 there is no need to suppose that that 5,218 of them were massacred in a battle in 1705 to account for the loss of population over time.
And there are many accounts of epidemics of various old world diseases striking various Native American groups without any inherited immunity and killing, for example, half the population in month.
As a result many Native American groups declined at a rate closer to 50 percent each generation, so that after eight generations and 210 years they might number only 0.0039062 as many as their original number.
Columbus reached the New world in 1492. According to the US census the number of Native Americans in the USA declined until the period of about 1890 to 1900. So for about 400 years and 15 generations the overall population of Native Americans declined until they developed enough resistance to European diseases for births to exceed deaths.
Even old world people who had much greater inherited immunity against smallpox suffered greatly from it. During the 18th century smallpox killed an estimated 400,000 Europeans per year. Smallpox killed 5 European Monarchs during the 18th century. With about 11 monarchies and 4 to 10 successive monarchs in each, that comes to about 44 to 110 total monarchs, so 5 monarchs killed by smallpox means that 0.045 to 0.113 - four and half percent to over eleven percent of - all 18th century monarchs in Europe died of smallpox.
And several other old world diseases cause terrible epidemics in the new world.