The Inca and Aztec empires were heavily impacted by European exploration and colonization. The first impact was that when Europeans reached the Americas, the Incas and Aztecs were conquered which killed thousands of them and enslaved the ones that survived. These early conquests started in 1494, when Europeans started to spread around the continent they also spread diseases such as smallpox, typhus, diphtheria, influenza, and measles, these also killed thousands of Natives that did not have defenses, historians say that 95% of the Natives were killed.
For wealth (since Columbus brought back gold many explorers would search the "new world" for more of it) but also for gain of land and power. I hope I helped!!!!