The fall of the Aztec Empire came about due to the Spanish conquest of Central America. After some brief and violent contact in 1517, a Spanish force under Hernan Cortes arrived in 1519 to completely subjugate the Aztecs. After war and disease swept the empire, it fell in 1521.
A majority of the men in the Cortes expedition had no idea as to their true goal, with many believing they were there to establish relations with the Aztec Empire. Shortly after landing, when Cortes gave orders to attack, several of his men began a mutiny. Faced with a possible insurrection, Cortes had the expedition's ships scuttled and burned in the harbor to remove any possibility of return to Spanish lands in Cuba.
One of the major factors that weakened the Aztecs was disease brought by the Europeans. A soldier contracted smallpox from a slave in another expedition, and when the force was overrun by an Aztec raiding party, the man was killed and his possessions were looted. From that single infection, smallpox spread rapidly throughout the Aztec population, since they had no natural resistance to the virus. As many as 25 percent of the Aztec population eventually died from the disease.