It's very plausible. Perhaps Native American cities were in a uniquely bad spot. On the one hand, plagues spread more in cities than among nomads. But on the

It's very plausible. Perhaps Native American cities were in a uniquely bad spot. On the one hand, plagues spread more in cities than among nomads. But on the other hand their ancestors had not lived for millennia with such germs; especially not the particular ones which the Europeans brought. And maybe even the Bronze Age collapse was similar. Lots of cities then would have been populated by people whose ancestors had been nomads a few centuries ago. As the size and number of such cities grew, you could imagine some critical point is reached where devastating plagues recur.