How did the Aztec Empire rise and fall so quickly?

The answer

The Aztec Empire dominated central Mexico from 1428 to 1521, with its capital Tenochtitlan - built on an island in Lake Texcoco - supporting over 200,000 people, larger than any European city at the time. The empire used floating gardens (chinampas) for agriculture and a tribute system to control neighboring peoples. Hernán Cortés conquered it with just 600 Spanish soldiers by exploiting alliances with resentful subject peoples and, devastatingly, introducing smallpox, which killed an estimated 40% of the population.