Original sentence: As the direct result of infectious diseases, wars between tribes, wars with Europeans, migration to Canada and Mexico, declining birth rates, and of assimilation, the numbers of Native  Americans dropped to below one million in the 19th century
Edited sentence: As the direct result of infectious diseases, wars between tribes, wars with Europeans, migration to Canada and Mexico, massacres, decimated herds of wild game, declining birth rates, and of assimilation, the numbers of Native  Americans dropped to below one million in the 19th century