Following the Aztec’s founding and construction of Tenochtitlan in the Valley of Mexico in 1325 AD, they quickly established their authority across the other societies in the valley. Historians refer to this time period as the Aztec Empire, since the Aztec were constantly expanding throughout central Mexico. As well, for the two centuries that followed the initial construction of Tenochtitlan, the Aztec were ruled over by a series of leaders referred to as Huey Tlatoani. In the Aztec language of Nahuatl this translates to 'Great Speaker'. Each huey tlatoani ruled in different ways but they all oversaw the expansion of both Tenochtitlan and the Aztec Empire until the arrival of the Spanish conquistadors in 1519.
Itzcoatl became the leader of the Aztec in 1427 and became the fourth tlatoani of the Aztec people. He was the brother of Huitzilíhuitl and the son of Acamapichti. Itzcoatl reigned over the Aztec Empire from 1427 until 1440, and is best remembered as the leader who saw the Aztecs become the most powerful Mesoamerican society in the Valley of Mexico. For example, as leader he famously formed an alliance with two other societies in the area in order to overthrow their mutual rivals. The Aztecs, Texcoco and Tlacopan joined forces in 1428 to create the Triple Alliance. Together they fought against the Tepanec and challenged them for superiority in the Valley of Mexico. Over time the three were able to overpower all other societies in the Valley of Mexico. As well, the Aztec became the strongest of the Triple Alliance and Tenochtitlan became the center of power in the region. During the reign of Itzcoatl, Tenochtitlan grew considerably with new temples, public buildings, and causeways to the shore of Lake Texcoco. The Aztec Empire grew out of the Triple Alliance and spread at this time across large areas of Mexico. Itzcoatl died in 1440 and was replaced as tlatoani of the Aztec by his nephew Moctezuma I.