It's easy to forget how much disease aided in the European colonization of America.

"The Mayflower first hove to at Cape Cod. An armed company staggered out. Eventually it found a recently deserted Indian settlement. The newcomers—hungry, cold, sick—dug up graves and ransacked houses, looking for underground stashes of corn. [. . .] When the colonists came to Plymouth, a month later, they set up shop in another deserted Indian village. All through the coastal forest the Indians had "died on heapes, as they lay in their houses," the English trader Thomas Morton noted."

The native Americans didn't have the same natural resistances to the diseases the Europeans brought. At some points, Smallpox traveled so quickly through the native populations that whole villages would die before the Europeans even got there.