The Latin American History as taught by the school systems in the 1960's had the Aztec tribe as the poorest and smallest of the tribes of that part of North America. They were landless until one day while wondering through a swamp, they came upon an eagle sitting on a cactus eating a serpent (snake). This was a vision that one of their elders had dreamed of previously. They made that swamp their home and became the great tribe that the Spanish Conquered a few hundred years latter. The eagle on the cactus eating the serpent is the symbol on the Mexican Flag. There is also a book Aztec, by Gary Jennings that is a great read once you get past the sexual descriptions of meaningless fiction.
Well that's not very accurate considering there was a major city the capital of a major empire siting on that island in the swamp. See if you can find LA Capital: The Biography of Mexico Cit by Jonathan Kandell. It starts before the Aztecs took over and goes in to great detail about how they came to power, their religion, eating habits as well as their relations to other tribes. The book is about 700 pages in paperback with about 15% devoted to this topic.