Excerpts from Books and Wikipedia
The Aztec people called themselves 'Mexica.' They moved from the north into central Mexico in the thirteenth century. At that time, the Aztecs allied themselves with the dominant city-state of Azcapotzalco. Azcapotzalco was overthrown by the Aztecs led by the ruler, Itzcoatl. Itzcoatl was succeeded by Moctezuma in 1440. He ruled over five to six million people. [Furtado: 1001 Days] "Itzcoatl, the fourth Mexica king in Tenochtitlán, allied with Texcoco and Tlacopan, defeats Azcapotzalco. Signifies the birth of the Aztec Empire and the start of an aggressive expansion lasting 90 years. Itzcoatl and his men began burning historic hieroglyphic books of conquered states, rewriting history with the Mexica at its center." [Wikipedia: Timeline of Middle Ages]