This is MY America!

[Urbane Guerrilla]

Originally Posted by Flint

They lacked the pandemic biological advantage of more disease-ridden Europeans, as the Vikings came through the decontamination zone of frigid lands where nasty microbes cannot survive outside the human body. Incidentally, the same reason the Natives had no resistance to Europeans sicknesses, they had come through the decontamination zone of the Bering Strait, and peopled a continent with no resistance to common bugs.

Interesting point, but here's another that seems even more valid: Europe, Africa, and Asia are all land-connected and in each of these places, animal husbandry is practiced. Smallpox in particular is associated with keeping cattle, as in all likelihood it's a small mutation of cowpox. Waves of smallpox infections can travel back and forth from one end of a continent and then back, like reflected waves off a seawall. Multiple continents, inhabited by humans, seem to mean a deeper pool of varied human diseases. Add in some other vectors (by a roll of the genetic dice) and look what you come up with.

Nor did it, we suspect, all go one way. In the early 1490s, syphilis, then present in Europe, suddenly turned virulent and a plague of it swept across the Continent. The timing seems more than a little suspicious.