When did the aztecs become the most powerful?

The Aztec empire of 1519 was at its  most powerful period. It was at this time the most powerful  Mesoamerican kingdom. It was a multi-ethnic and multi-lingual realm  that stretched for more than 80,000 square miles through many parts  of  what is now central and southern Mexico.

 This enormous empire reached from the pacific ocean to the Gulf coast and from central Mexico to the present - day republic of Guatemala. 

The population was 15 million people, living in 38 provinces and residing in 489 communities, which paid tribute to the Emperor Moctezuma II in Tenochtitlan, the capital city of the great empire. 

it increase by 12% a year from 1812-1820