The Mexica were presumably a people from Northwestern Mexico/Southwestern United States, of course, before either Mexico or the United States were conceived. Their nomadic existence led them to a great number of encounters with other natives living similar existences, sans nomadism. Once the Mexica reached the basin of Mexico, they began to put down roots, however difficult it may have been. Eventually, their warrior-like way of life earned them “jobs” as mercenaries, essentially doing the dirty work for those that were established there. This allowed them to A) further earn respect and a reputation throughout the valley area as a tough, warrior-like people who were resilient in times of battle, and B) earn a stake in the area. Their cultural developments mishmashed with that of the other inhabitants of the Valley of Mexico.
The Aztecs were Mexicas specifically from Tenochtitlan, who were devote followers of the Mexica God, Huitzilopochtli, who originally led them to inhabit an island in southern Lake Texcoco, in the Valley of Mexico. The Aztecs of Tenochtitlan soon became the dominate Mexica people in all of the area, taking over more “towns”, land and resources than any other, along with their Mexica allies in the nearby cities of Texcoco and Tlacopan, also known as the “triple alliance”. They commanded conquered peoples in the area to pay tribute in goods, crops, women, and other necessities. Scholars have viewed this as a sort of tax system. If I may, I would probably compare this a little bit to “taxation without representation”. 😉 The Aztecs were truly gifted in a number of ways and have left a long-lasting legacy, which researchers have studied extensively since the Spanish “discovered” them in 1521. They had grander canals than that of Venice, and an ingeneous earth-enriching gardening technique called ‘chinampas’ farming, in which they dredged Lake Texcoco’s extensive lakebeds to fertilize and build agricultural islands. Several of the Aztec nobility took it upon themselves to re-write a selective history throughout their time of dominance. When doing so, it is thought that they largely destroyed the bulk of historical accounts and specimens to preserve their glorification throughout time.