Final answer:
Before the Spaniards arrived, a civil war coupled with the introduction of smallpox by Europeans significantly weakened the Inca Empire, paving the way for Pizarro's conquest and the eventual fall of the empire.
Step-by-step explanation:
Before the Spaniards arrived, a civil war took place that led to the fall of the Inca Empire. This internal conflict was between the two sons of Huayna Capac, the late Inca leader. The civil war, coupled with the devastation caused by diseases such as smallpox introduced by Europeans, significantly weakened the once mighty empire. This strife allowed Francisco Pizarro and his small force of conquistadors to capitalize on the chaos, leading to the eventual capture and execution of the Inca ruler Atahualpa in 1533, and the collapse of the Inca Empire in 1535.