The Fall of the Inca Empire
Francisco Pizarro reached Peru with fewer than 200 men and captured the largest empire in the Americas within a year. He arrived at the perfect moment: smallpox, spreading overland ahead of any European, had already killed the Inca emperor and his heir, plunging the empire into a civil war between two brothers. Pizarro seized the exhausted victor at their first meeting. Again the decisive weapons were disease and a succession crisis — an empire that fell not because it was weak, but because it was caught mid-collapse.
A sudden collapse in population (plague, famine, mass violence) creates labor scarcity that reorders economy and society.