It's been a long time since I've read any pre-Columbian history, but I seem to remember that in addition to infectious disease, a lot of the South American empires were easy to conquer because the subjects generally hated their rulers, and the Spanish had no trouble finding indigenous allies.
It's been a long time since I've read any pre-Columbian history, but I seem to remember that in addition to infectious disease, a lot of the South American empires were easy to conquer because the subjects generally hated their rulers, and the Spanish had no trouble finding indigenous allies.