The Aztec period city-state of Otumba in the upper Teotihuacan Valley was integrated into the Acolhua domain from the early 1430s to about 1515. It then became independent, demonstrating the fragility of city-state organization as a means of regional political integration. A close look at Otumba and other city-states in the Teotihuacan Valley reveals that Acolhua strategies of social engineering welded together the potentially-autonomous city-states into an elaborate political system with impressive structural strengthening and improved flow of services and materials through it.