The Spanish didn't stop with the Aztecs, however. They conquered many more peoples who were less cruel and warlike than the Aztecs. But lest we slam Spain too much, we can't forget the Portuguese, teh Dutch, the British, and of course, ourselves. Neither do we have to look only in the Western Hemisphere, more technologicaly "advanced" cultures have a memorable history of slaughtering, conquering, and otherwise oppressing other cultures on every continent except Antarctica. This behavior is not limited to one skin color, religion, language group, or whatever. Everybody joins the fun eventually. The formerly oppressed one day rise to become the new oppressors.
Just the way we are.