The Great Dying refers to the massive mortality that occurred in the Western Hemisphere in the fifteenth and sixteenth centuries as a result of the European invasion. While people from both the Eastern and Western Hemispheres died in battle and as a result of violent conflicts, disease was by far the major cause of death. Because of the separation of the two halves of the world, indigenous people had no resistance to numerous diseases that the foreigners brought. While it is common to think of all the invaders as European, many of the foreigners were from North Africa and the Middle East. Smallpox was most likely the largest single killer.
Although there are no accurate records of the population in those years, numerous estimates have been made of the total population as well as the number and percentage of deaths. The higher estimates are about eighty percent mortality in the first few decades. In addition, many people were at least temporarily disabled from illness, and the devastating effects on women in their reproductive years both increased the infant mortality rate and reduced population growth. Rulers were less able to mobilize effective, full-size armies and to defend their territory. It is believed that smallpox reached the Inca Empire via indigenous carriers before the Spaniards actually arrived in Peru and that the disease probably killed Emperor Huayna Capac. The resulting civil war between his two sons, Huascar and Atahualpa, divided the empire and facilitated the Spanish takeover.