The fall of the Aztec Empire culminated in the Siege of Tenochtitlan, where Spanish conquistador Hernán Cortés and his indigenous allies (such as the Tlaxcalans) defeated the Aztec Emperor Cuauhtémoc. The victory was made possible by a combination of superior weaponry (steel and gunpowder), tactical alliances with local tribes who resented Aztec tribute demands, and the devastating impact of smallpox, which decimated the population of the capital. Tenochtitlan, one of the largest and most advanced cities in the world, was largely destroyed and later rebuilt as Mexico City. This event marked the beginning of Spanish colonial rule in the Americas and the end of one of the world's most sophisticated indigenous civilizations. It initiated a total transformation of Mesoamerican culture, religion, and demographics, setting the stage for the creation of New Spain.