What caused the end of the aztecan civilization?

The defeat of the Aztec king and army in 1521 AD by the Conquistadors under Hernán Cortés ended the Aztec Empire. But contrary to what many people think, Aztec civilization did not disappear. Although Roman Catholicism quickly became the dominant religion, the Aztec people continued to exist as before, keeping much of their cultural heritage and speaking the Aztec language, even to this day. Although Mexicans from different national and cultural backgrounds now co-exist , in several regions the Mayas still are a dominant presence.