The Aztecs were a nomadic people who roamed around Aztlan for a long time prior to the 1200's.
Eventually, the Aztecs migrated into the Valley of Mexico. Since they were considered barbarians and often disparaged by other communities, they were forced to move to different parts the valley and serve as mercenaries.
The Aztecs were told by a priest that they should build their capital where they saw an eagle perched on a cactus eating a serpent. This would be a sign from the gods that it would be a good location to settle their community.
The Aztecs saw the eagle on a cactus and began to build their capital city. This location was on a small island in Lake Texoco, near Azcapotzalco.
The Aztecs began to expand their empire, but found that it lacked land. They built Chinampas, or floating islands, with soil and mud, and used those for agricultural and living purposes. Additionally, they created roads and canals to travel to other city-states and places within the empire.
The Aztecs used the resources available to them for their benefit. They traded many items from Lake Texoco, including a special type of algae called spirulina. This resourceful quality helped the Aztecs create a very successful civilization.