When one thinks about "ancient" Native American civilizations and ruins... the thing is that... most of them, they weren't ancient. The Inca were not fully conquered by the Spanish until 1572... for reference, the Mona Lisa was painted in 1502 and Martin Luther made the 95 Theses in 1517.. the "ancient" Aztec Empire was younger than the university of Oxford founded in the 11th century, Montezuma lived at the same time than Leonardo Da Vinci... There are castles that are younger than Machu Picchu, those cities were inhabited by millions just a few centuries ago, and some (Cuzco, México), many actually, are still inhabited today. People speak about the Ancient Maya as if it was some mysterious civilization that was lost, and while it was past its prime at the time of European conquest, the Maya still had city-states and were living in the same areas they live today.
There are still millions of people, right now, who speak Quechua, Nahuatl, and Maya in all their dialects, and I'm just talking about the three most well-known civilizations here... there are millions of Native Americans who still speak their languages and practice their culture and beliefs alive, both thriving and struggling today.
Talking about the "Ancient Inca" or "Ancient Aztecs" makes as much sense as talking about the "Ancient Dutch" or the "Ancient Swedes", and it's another way of erasing them, saying that they just aren't around anymore just like say the Sumerians, or that they just weren't relevant to world history. They were contemporaries to modernity and they're still alive today.
You can talk about the Ancient Olmecs or Ancient Chavín though. Because the Inca and the Aztecs are relatively "modern" but their cultures were just the latest from a cycle of civilizations stretching millenia before Christ.
