Before the Spanish conquest, the Aztec civilization controlled trade routes from the Pacific Ocean to the Gulf of Mexico and as far south as Guatemala. Its rich and populous empire was held together by marriage alliances and ritualized battles in which large numbers of enemy warriors were captured and sacrificed to honor and sustain the gods. When Hernán Cortés sailed from Cuba to claim the Mexican mainland for Spain in 1519, he could not have anticipated the odds against him and his small force of 600 foot soldiers and 15 horsemen. His ultimate success in subduing the Aztecs was in large part due to the help of a Nahua slave woman called La Malinche, who became his chief interpreter, advisor, and the mother of his firstborn child. She advised Cortés on the weakness of Aztec alliances with other indigenous groups, their respect for ruthlessness, and their preference for capturing rather than killing their enemies in battle. Cortés used this information to defeat an army that was better supplied and much larger than his own. After God, he said, La Malinche was his most important ally.
Cole TB. La Malinche (Young Girl of Jalala, Oaxaca). JAMA. 2012;307(12):1233. doi:10.1001/jama.2012.342