Why did diseases like smallpox kill off Native Americans and not the European populations responsible for transmitting (le spreading around infecting others) it?

Europeans were immune

Explanation:

Europeans had already had and survived the diseases but they were still able to transport it.

norsemen from northern countries had made earlier journeys

the lowest among the social higher rank were the working class. this class remained detached to the political progression   of the country and was hostile to the other two classes