The Spanish conquest of the Americas contributed to Jared Diamond's theory of guns, germs, and steel. During the conquest, the Spanish had technological advantages like guns and steel weapons that helped them defeat American civilizations. They also unwittingly introduced deadly germs like smallpox to which Native Americans lacked immunity, resulting in widespread epidemics and death. The smallpox outbreak that hit Tenochtitlan weakened the Aztec capital city and aided the Spanish conquest. Diamond's theory posits that differences in access to technology and resistance to diseases gave European societies advantages in conquering other parts of the world.