Final answer:
The Aztecs were captured by the Spaniards, significantly helped by the spread of smallpox, which decimated the Aztec population and led to the fall of Tenochtitlán. The siege was supported by Tlaxcalan allies and exploited the weakness caused by the epidemic and famine.
Step-by-step explanation:
The Aztec captured by the Spaniards were facilitated in part by internal divisions within the region, but what truly aided the Spanish conquest was the spread of smallpox among the Aztecs. An African slave who was part of a Spanish expedition introduced smallpox to the native population in April 1520. The indigenous peoples had no immunity to the virus, leading to a rapid and devastating outbreak. By September 1520, smallpox had reached Tenochtitlán, causing widespread death and weakening the Aztec defenses. In May 1521, Cortés and his Indigenous allies, which included a significant force from the Tlaxcalan people who were opposed to Aztec rule, returned to lay siege to the weakened city. The siege, lasting three months, resulted in Tenochtitlán's fall. The Spanish took advantage of the decimated Aztec army, largely due to the disease, and the subsequent lack of food in the city due to incapacitation of its inhabitants. The capturing of the Aztecs marked the beginning of Spanish colonization and the widespread conversion of the native population to Christianity, as well as large-scale cultural and socio-political changes.