Moctezuma learned that Cortés was getting support from old enemies. He tried to talk Cortés out of coming to Tenochtitlán and even sent magicians to cast spells on the Spaniards. But Cortés and his men marched on. Moctezuma at last accepted that he could not stop the Spaniards. So he decided to welcome them as honored guests.

For a while, all was peaceful in Tenochtitlán. The Spaniards, however, grew nervous. They knew they were greatly outnumbered and that even their superior weapons could not keep them safe. They took Moctezuma hostage. In addition, they demanded that the emperor order the Aztec to stop sacrificing to their gods. Moctezuma refused. A few weeks later, fighting broke out. The Spanish grew fearful that the Aztec priests were plotting against them. The Spaniards attacked and killed hundreds of priests during a
religious ceremony. The Aztec responded by trying to wipe out the Spanish. Many men were killed on both sides. Among the victims was Moctezuma himself. The Spaniards then fled Tenochtitlán.

The Spaniards rebuilt their army by enlisting more of the Aztec’s old enemies. In 1521, Cortés and his allies surrounded the capital. With no supplies coming into Tenochtitlán, city residents began to starve. An outbreak of smallpox also swept through the city. This disease was carried by the conquistadors. The Aztec had no immunities against European diseases. As a result, the diseases hit very hard and spread quickly. Warriors, commoners, and nobles alike died in the epidemic.

In May of 1521, Cortés organized a final bloody attack. Spanish forces, armed with guns and cannons and joined by thousands of native allies, advanced along the causeways. The Aztec fought bravely but were overwhelmed by their attackers. Meanwhile, the smallpox epidemic left thousands dead or dying in the streets. Others were too sick to fight. Tenochtitlán fell in August of 1521. The once-great city lay in ruins, and the mighty empire of the Aztec was defeated.