The Aztec empire, which controlled some 11,000,000 people, had always had to deal with minor rebellions - typically, when new rulers took power at Tenochtitlan - but these had always been swiftly crushed. The tide began to turn, though, when the Aztecs were heavily defeated by the Tlaxcala and Huexotzingo in 1515 CE. With the arrival of the Spanish, some of these rebel states would again seize the opportunity to gain their independence. When the conquistadors finally did arrive from the Old World sailing their floating palaces and led by Hernán Cortés, their initial relations with the leader of the Aztecs, Motecuhzoma II, were friendly and valuable gifts were exchanged. Things turned sour, though, when a small group of Spanish soldiers were killed at Tenochtitlan while Cortés was away at Veracruz. The Aztec warriors, unhappy at Motecuhzoma's passivity, overthrew him and set Cuitlahuac as the new tlatoani . This incident was just what Cortés needed and he returned to the city to relieve the besieged remaining Spanish but was forced to withdraw on the 30th of June 1520 CE in what became known as the Noche Triste . Gathering local allies Cortés returned ten months later and in 1521 CE he laid siege to the city. Lacking food and ravaged by disease, the Aztecs, now led by Cuauhtemoc, finally collapsed on the fateful day of 13th of August 1521 CE. Tenochtitlan was sacked and its monuments destroyed. From the ashes rose the new capital of the colony of New Spain and the long line of Mesoamerican civilizations which had stretched right back to the Olmec came to a dramatic and brutal end.