When the conquistadors returned to Peru in 1532, a war of succession between the sons of Sapa Inca Huayna Capac, Huáscar and Atahualpa, and unrest among newly conquered territories weakened the empire. Perhaps more importantly, smallpox, influenza, typhus and measles had spread from Central America. The first epidemic of European disease in the Inca Empire was probably in the 1520s, killing Huayna Capac, his designated heir, and an unknown, probably large, number of other Incan subjects.