By Native Americans, I mean all pre-Columbian inhabitants of the Americas, from the Arctic to Tierra del Fuego. In OTL, many of the different native cultures succumbed to Old World diseases they never could have developed immunity for, up until that point (due to a multitude of factors)...
15th century
castaways
castaways in the new world
diseases
earlier discovery of the americas
immunity
native americans
natives
old world diseases
preventing tragedy