I believe the theory is that Europeans kept various domesticated animals and Native Americans had far fewer, and that those animals were frequently sources of n

I believe the theory is that Europeans kept various domesticated animals and Native Americans had far fewer, and that those animals were frequently sources of new diseases. Europe was also more interconnected, so diseases may have spread farther while Native diseases died out. See the wiki page: https://en.m.wikipedia.org/wiki/Native_American_disease_and_epidemics https://en.m.wikipedia.org/wiki/Native_American_disease_and_...