Why did the Moche empire fall?

Civil war
Although the military cunning and advanced military technology of Spanish Conquistadors (military adventurers) such as Pizarro is usually seen as the main reason for the fall of the Inca Empire, it in fact only allowed the Spanish a rather precarious "first foothold" in Peru. The Spanish struggled another 40 years to secure control of the Inca empire and almost lost their initial advantage at one point. Scholars now view the fall of the Inca Empire as somewhat fated by the time the Spanish arrived, as by that point, it was depopulated and militarily weakened through Civil War between two rival claimants to the Imperial Inca throne - Huascar and Atahualpa. The Civil War was just concluding when Pizarro's group entered the scene, and the victor - Atahualpa - did not believe the Spaniards posed a serious threat. Another major factor was smallpox. This and other diseases introduced by contact with Europeans spread rapidly across the New World, ahead of the Conquistadors, reducing the capacity of Indian populations to fight the invaders.