Native Americans had only stone and wooden weapons and no animals that could be ridden. Those military advantages repeatedly enabled troops of a few dozen mounted Spaniards to defeat Indian armies numbering in the thousands.

F. 2005 Collapse: How Societies Choose to Fail or Succeed. PMID 3762700.

Originally trained in physiology Diamond's work is known for drawing from a variety of fields including anthropology ecology geography and evolutionary biology. He is currently Professor of Geography at the University of California Los Angeles.