The Columbian Exchange
Francisco Pizarro (1475-1541) was one of the most successful Spanish conquistadors. In 1532, Pizarro led a small force of Spanish soldiers and conquered the mighty Inca Empire. He then founded the Spanish colony of Peru, ruling former Inca territories there until he was assassinated by followers of a rival conquistador in 1541.
The ecological processes of the Columbian Exchange gave Pizarro a vital advantage in his conquest of the Inca Empire. A catastrophic smallpox outbreak in 1525 killed nearly a quarter million Inca, including the emperor and many of his most powerful aides and generals, leading to a power struggle among the survivors that devolved into civil war. When Pizarro invaded a few years later, he faced much less resistance than he would have prior to the epidemic.