What is the significance of empires like those of the Aztecs and the Incas in world history?
The Aztec and Inca empires are not significant in the history of the world in the same way that things like the Glorious Revolution and the Declaration of the Rights of Man (which you asked about in other questions) are. This is because these empires did not have the ability to remain in power after European contact and to shape the greater world.
Of course, the Aztec and Inca empires were extremely significant to those who lived in them and around them. They are also significant today as things for their descendants to be proud of and to rally around. We can see this, for example, in the popularity of Aztec imagery in modern Mexico.
Even so, these empires did not go on to make a great impact on the world as a whole. Their ideologies and customs did not spread, at least in part because they did not colonize vast areas on many continents. Their weakness (relative to that of the Europeans) prevented their empires from having a major impact on world history.
All this is not to say that the Aztecs and Incas were racially inferior or that there is no reason to learn about them. However, it remains true that it is the societies with the most military and economic power that have had the most impact on world history. The Aztecs and Incas lacked those things and therefore were unable to have a huge impact on world history.