Aztec's had a very powerful empire. The main job of the ruler was to take over more territory and maintain it. He was in charge of the military and it was his job to lead successful military conquests. One of their main goals was to take over other tribes in order to gain more land for themselves. They did, however, let the conquered tribes continue to live on their own but these conquered tribes had to follow Aztec law. The more land a ruler conquered, the more powerful he became. If he wasn't able to conquer more land, he would be replaced with a new ruler. The goal was expansion.