Final answer:
Moctezuma I turned to Hernán Cortés for help against flooding in Tenochtitlán. Cortés laid siege to the city and captured it by exploiting the disunity among the groups in the Aztec Empire.
Step-by-step explanation:
Moctezuma I turned to the Spanish conquistador Hernán Cortés for help against flooding in Tenochtitlán. Cortés, who had already established alliances with native peoples who resented Aztec rule, laid siege to the city and eventually captured it in August 1521.
The Spanish were able to capture Tenochtitlán by taking advantage of the disunity among the diverse groups in the Aztec Empire.