Comment by larksimian
1 day ago
It's not really random. Disease development in the Old World was a combo of long term urbanisation and animal husbandry. Urbanisation in the New World existed but wasn't as old and obviously there was way less animal husbandry. Also assuming the Bering straight crossing hypothesis humans probably left almost every freaking old world parasite and disease behind by the time they got into the americas. Hundreds of thousands or even millions of years of eveolution of diseases that evolved in Africa/Eurasia pretty much gets purged during that migration.
Sure, "random" isn't the right term for what I mean.
There were reasons, but neither side understood them!
From their perspective, it just so happened that 80-90% of the population on one side died within weeks of contact. Often the disease travelled faster than the invaders, so as the went inland they found mostly empty settlements they could just take over.
It's easy to see how both sides could think that the god(s), in their inscrutable ways, had decided to give the land to the Europeans.
This also played out in the opposite direction in Africa. There the Europeans just couldn't survive for long until Malaria treatments became available in the mid 1800s, and so Africa was colonized last. Since Africa is where humanity originated, it has the most diseases and parasites that specialize in feeding on us.
Many of the diseases that afflicted the old world may have evolved after humans crossed into North America, so there was never any resistance in the New World.