Empire and imperialism: Aztec and Inca

Did empires help to shape world history? There have been various types of empire. One was the archaic type. Of the few American examples, the Aztecs and Incas are the best known. Both had features in common with Old World cases such as the Assyrian, Han or Roman empires and both were certainly imperialist but their structures and policies differed from each other markedly. Did they have similar effects, then? Or has their historical significance been exaggerated on account of their mighty monuments? What do the Aztecs and Incas suggest about Old World empires?