What happened to the Incas and the Aztecs?

Answer 1

Both, in part, fell victim to the colonial interests of Spain. Hernán Cortéz arrived in the Aztec empire in 1519 and allied himself with a Confederacy opposed to the capital, Tenochtitlan, which ended in the eventual destruction of the city in 1520 and the slow collapse of the native government. From 1520-1521 a smallpox outbreak killed 10-50% of the population of the capital, undoubtedly aiding in its downfall, and later epidemics of smallpox and typhoid had reduced the Aztec population by 80% in just 60 years.

A similar story goes for Francisco Pizarro, who arrived in Peru in 1532 to conquer the Incas right as a smallpox outbreak and a civil war were happening. Pizarro and his men allied with one side and were able to make alliances to overthrow the ruler and install themselves in the seats of power. The Inca were hit with wave after wave of epidemics of European origin, wiping out 60-94% of the population. Between these diseases and the harsh conditions of Spanish rule, the vast majority of the Incan culture died out.