What happened to the Aztec Empire upon the arrival of the Spanish?

Upon the arrival of the Spanish in the early 16th century, the Aztec Empire faced a rapid decline due to a combination of military conquest and the introduction of diseases like smallpox, which decimated the indigenous population. Spanish conquistador Hernán Cortés, aided by indigenous allies who opposed Aztec rule, captured the capital city of Tenochtitlán in 1521. This led to the fall of the Aztec Empire and the establishment of Spanish colonial rule in the region. The cultural and political landscape of Mesoamerica was drastically altered as a result.