The Aztec first arrived in the Valley of Mexico as migrants from the north, following the collapse of the Toltec Empire around 1150. Warlike hunter-gatherers, they gained a niche as mercenaries for the cluster of city-states which controlled the region, often forced to uproot when they outstayed their welcome. Eventually, they gained sanctuary on the islands of Lake Texcoco where, in 1325, they founded their capital, Tenochtitlan. In their travels, they appear to have made contacts with Toltec refugees; they would come to see themselves as heirs of the Toltec, who were their cultural and political mentors. Their imperial take-off occurred under the rulers Itzlcoatl (1428–40) and Moctezuma I (1440–69), who leveraged alliances with other city-states to first dominate the Valley of Mexico then to extend their dominion to the Caribbean and Pacific. They even had a tributary in modern Guatemala where they coincided with the waning Itza Maya.
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