The demise of the Inca Empire was very similar to that of the Aztecs.

     The collapse of the Aztec empire,was predominantly due to the increasing need of human sacrifice. According to Conrad and Demarest, the Aztecs, "had actually pushed the outer boundaries of the empire beyond the limits of its internal structures ability to administer or even hold their conquests" (61). In other words, as the Mexica marched through Mesoamerica conquering peoples with the main goal of having more sacrifice, and established virtually no governmental stability within their territories. When the Spanish invaded their territory, although not an easy task, the Aztec instability was one of the factors that led to their collapse.  

      Similarly, the Inca were politically unstable due to their emphasis on ancestor worship. Through the process of split inheritance, deceased kings maintain their power and all property rights even after death, leaving two proprietors to deal with their affairs. This caused two issues: One, in order for anyone to acquire wealth or territory they had to conquer new land. Two, many people began to argue that the deceased had to much power. The civil war between Huascar, who Conrad and Demarest state, "knew exactly what lay at the heart of Tawantinsuyu's problems-the property rights of the dead" (136), and Atauhualpa took place at the most inopportune time. While the Inca were battling over the issue of split inheritance they failed to see the warning signs and prepare themselves for and even bigger enemy, the Spanish Empire.
     An empire can only maintain stability if it has a strong government and resources to support it's citizens. The Aztecs' search for blood and with every new Inca ruler's search for land, both empires extended far past the realms of being able to maintain political stability or an economy that would maintain their citizens. The Spanish Empire had only the task of finding the tribes that were upset with their perspective empires and ask them to rise up and defeat them.