Ah, yes, I think some of you may have thrown a little cold water on my "Native populations 5-9x higher than OTL theory. The far Northwest is a "bad" place for an epidemic to start, because the area is sparsely populated and I think the population would be mostly hunter-gatherers around 1000 (and later).
Still, it might take epidemics hundreds of years to make their way all the way to Central America, at which time there will be agricultural civilizations there.
The epidemics have to make their way down to the the Mississippi River Valley or Mesoamerica and South America, which are the places where the population is sedentary and high enough to create the disease reservoirs, resulting in repeating epidemics like the ones Europe went through, which would confer immunity on the descendent populations hundreds of years later. Via trade these epidemics would probably also spread to the outlying migratory tribes in North America.
It's is important to remember that the Mississippian societies of North America appeared to be in decline when De Soto made contact. Archeology indicates that civilization peaked around 1200-1400. It began around 1000, so when the Vikings settled Vinland around that same time, I don't think it is far fetched to assume that the Mississippi River and its tributaries were not already being used as a communication and transportation highway. Of course the native population was not quite as high in 1000 as would be three centuries later, but I don't think that necessarily means the spread of diseases would necessarily be as limited as you suggest.
I've heard that Cahokia and the rest of the Mississippian culture were in decline due to the effects of the Little Ice Age causing crop failure and increased inter-city warfare due to the food shortages creating a vicious cyle, etc, etc. But of course that's just a theory. At any rate the population of Mississippian cities was definitely higher in the 1200s and 1300s than it was at the time of the Exchange.
Well that's true, but more people = more trade = more contact. I'm not entirely sure what the evidence shows about when and how badly western native tribes were hit as opposed to more eastern populations..<snip>
Yeah, on further thought here's my biggest hangup about my own theory about Amerindian numbers being able to bounce back to pre-contact numbers. I can distinctly remember reading that of the West Coast Natives Lewis and Clark had visited in the 1790s, 75% would die of disease epidemics within the next 50 years. (Not because of the expedition, just because of the general spread of disease). I know there was also an extremely deadly smallpox epidemic in the interior of the continent in the 1770s. (Which had started in, and also killed many in the American colonies, but at nothing like the death rate it was killing Indian tribes in the middle of the continent)
What this means is that there must have been incredibly deadly European disease epidemics hundreds of years
after there were already known epidemics in the region, such as the one that wiped out the Mississippian Culture in the late 1500s, meaning that like Unconsensual was saying, a one-time burn-through apparently doesn't confer a lot of resistance on descendent populations. Although if anyone knows more about this or has information about which tribes were affected by the 1770s epidemic I'd love to hear it.
Anyway, in conclusion I think my 5-10 times larger Amerindian population estimate might be a little high, and something more like 2-4 times OTL's might be more realistic. That's
still a huge difference than OTL, though.