What are three unanswered questions historians have about the Incas/Mayans/ and/or Aztecs?

Question

What are three unanswered questions historians have about the Incas/Mayans/ and/or Aztecs?

Answer 1

I'd agree with icabod...how did the Inca's build Machu Pichu with some stones that weighed over 60 tons in a mountainous area and get such precise fitting in irregular shaped rocks...most of them cannot have a razor blade or thin knife inserted between them.

Answer 2

Whether the Book of Mormon can be used as a reliable Anthropological document, to prove that the Jaredite, Nephite and Mulekite migrations (circa 2200-600 B.C.) from the Middle East, can be responsible for the existence of Haplogroup "X", Blood Types "A" & "B", and pyramid-building in Central America, as well as the 30% occurrence of Hebrew and Aramaic vocabulary root words, in the Ute-Aztecan language family-group!

Answer 3

For the Incas I'd like to know the method they used to create their precise fitted stone walls.

With all three groups I'd like to know just what started them off on  the path to civilization.

The Maya abandoned their cities and left them to the jungle. What happened?