The Aztecs ruled a large empire in Mexico until the arrival of Spanish conquistador Hernan Cortes in 1519. Cortes led a small expedition that was received peacefully by the Aztec ruler Montezuma, but Cortes then launched a surprise attack, killing many Aztecs and capturing Montezuma. Without Montezuma to lead them, the Aztec empire quickly collapsed. European diseases also devastated the native population. Cortes declared himself ruler of Mexico and the surrounding lands, and he lived a life of great wealth while most native people were enslaved or died from disease.