Moctezuma solidified the alliance with two neighboring peoples, Tlacopan (a small sovereign kingdom) and Texcoco. In this skillfully crafted Triple Alliance, 4/5ths of a newly conquered territory would be divided between Texcoco and the Aztecs, with the remaining 1/5th given to Tlacopan.

Among the Aztecs' greatest achievements, Moctezuma I and Nezahualcoyotl of Texcoco organized the construction and completion of a double aqueduct pipe system, supplying the city of Tenochtitlan with fresh water.

Moctezuma extended the boundaries of the Aztec empire beyond the Valley of México to the Gulf Coast, subjugating the Huastec and Totonac peoples and thereby gaining access to exotic goods such as cocoa, rubber, cotton, fruits, feathers, and seashells.

Circa 1458, Moctezuma lead an expedition into Mixtec territory against the city-state of Coixtlahuaca, the pretext being the mistreatment of Aztec merchants. Despite the support of contingents of Tlaxcala and Huexotzingo warriors, traditional enemies of the Aztecs, the Mixtecs were defeated. While most of the defeated chieftains were allowed to retain their positions, the Mixtec ruler Atonal was ritually strangled and his family was taken as slaves. The Codex Mendoza records that the tribute owed by Coixtlahuaca consisted of 2000 blankets (of 5 types), 2 military outfits with headresses and shields, green gemstone beads, 800 bunches of green feathers, 40 bags of cochineal dye, and 20 bowls of gold dust.

Similar campaigns were conducted against Cosamaloapan, Ahuilizapan (Orizaba), and Cuetlachtlan (Cotaxtla).