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Triple Alliance civilization

With the decline of the Toltec civilization came political fragmentation in the Valley of Mexico. Into this new political game of contenders to the Toltec throne stepped outsiders: the Mexica. They were also a desert people, one of seven groups who formerly called themselves "Azteca", in memory of Aztlán, but they changed their name after years of migrating. Since they were not from the Valley of Mexico, they were initially seen as crude and unrefined in the ways of the Nahua civilization. Through political maneuvers and ferocious martial skills, they managed to rule Mexico as the head of the 'Triple Alliance' which included two other Aztec cities, Tetxcoco and Tlacopan.

Latecomers to Mexico's central plateau, the Mexica thought of themselves, nevertheless, as heirs of the civilizations that had preceded them. For them, arts, sculpture, architecture, engraving, feather-mosaic work, and the calendar, were bequest from the former inhabitants of Tula, the Toltecs.

The Mexica-Aztecs were the rulers of much of central Mexico by about 1400 (while Yaquis, Coras, and Apaches commanded sizable regions of northern desert), having subjugated most of the other regional states by the 1470s. At their peak, the Valley of Mexico where the Aztec Empire presided, saw a population growth that included nearly one million people during the late Aztec period (1350–1519).

Their capital, Tenochtitlan, is the site of modern-day Mexico City. At its peak, it was one of the largest cities in the world with population estimates of 200,000–300,000. The market established there was the largest ever seen by the conquistadores on arrival.