> What finished many of them off was a lack of resistance to smallpox, which was brought over by the first explorers/colonists. They lacked herds of domesticat

> What finished many of them off was a lack of resistance to smallpox, which was brought over by the first explorers/colonists. They lacked herds of domesticated animals, which not only held them back agriculturally, but were also the source of diseases like smallpox.