When they arrived in Mexico, the Spaniards imprisoned many captives and later founded a town called La Villa Rica de la Vera Cruz, now called Veracruz. One of the prisoners, Malinche, became his lady and acted as a guide and an interpreter. Cortez established an independent government and only recognized the authority of the Spanish crown. Once the town stabilized, he initiated his progression inward. He defeated a tribe known as the Tlaxcalans and then formed a treaty with them against the Aztecs. Immediately ensuing a meeting with Montezuma II, Cortez decided to enter Tenochtitlan, the Aztecs' capital. Some Aztecs believed that Quetzalcoatl, a god, with light skin, and a beard, had returned from the east as Cortez. Montezuma, instead of resisting Cortez, allowed them to gain access to the city so he could perceive their motives.

Once in the city, the Spaniards took Montezuma hostage, and made him pay an enormous ransom of gold and jewels. Along with about 600 native associates, the Spaniards set up base in one of the Aztec's many ceremonial temples. During all these events, Governor Velazquez sent a fleet under soldier Panfilo de Narvaez to Mexico. Cortez knew of this and marched with a small group to the coast where he captured Panfilo de Narvaez, and persuaded most of the soldiers to join his band. When they returned to Tenochtitlan, an Aztec revolt had progressed too far. Montezuma died from a stoning three days after asking the Aztec people to calm down. On June 30, 1520, a dark rainy night known as Noche Triste, the Spaniards retreated from the city.

After defeating a large number of Aztecs, he went to the Tlaxcalan tribe and reorganized his army. Cuauhtemoc, the new ruler, fell with the city Tenochtitlan on August 13, 1521. Cortez then erected Mexico City on top of the ruins of Tenochtitlan. Immigrants moved in and the city became the most important Spanish city in the Americas. New Spain elected Hernando Cortez as its governor and Captain general in 1523. He also discovered the Baja California peninsula in 1536. Fearing his ambition, the Spanish Court revoked his two positions as well as his rights and property. In 1530, Cortez married the count of Aguilar's daughter and returned to Mexico. Most of his fortune and his ship went down with the unsuccessful expedition to Algiers in 1541. On a plot of land near Seville, he died in 1547. He is also known as Hernán Cortés.