What if...

[magid]

... there were as many virulent diseases that affected European immigrants in the to-be United States as they brought with them? Would there have been a U.S.? Or more of a patchwork of smaller political entities, perhaps with a confederated region of different tribes through much of the western plains?

And why was the situation so unbalanced, anyway? Was it because the Europeans were coming from cities, which encouraged disease, so the Natives were comparatively disease-free?