When settlers first found America, they unintentionally decimated the natives with foreign diseases, so shouldn't the settlers have brought native diseases back to Europe upon return?

by majestic_failure
Georgy_K_Zhukov

Always more to be said here, but this FAQ Section might be of interest for you.

terminal_veracity

This is covered by /u/anthropology_nerd here:

https://www.reddit.com/r/AskHistorians/comments/3jll9c/one_of_the_main_reasons_europeans_were_so_utterly/cuqoepv/