The Aztec of Central Mexico built a tributary empire covering most of central Mexico. The Aztec were noted for practicing human sacrifice on a large scale. Along with this practice, they avoided killing enemies on the battlefield. Their warring casualty rate was far lower than that of their Spanish counterparts, whose principal objective was immediate slaughter during battle. This distinct Mesoamerican cultural tradition of human sacrifice ended with the gradually Spanish conquest in the 16th century. Over the next centuries many other Mexican indigenous cultures were conquered and gradually subjected to Spanish colonial rule.