The focus on Mesoamerican cultures
Whereas kingdoms like the Aztec and Incas were able to control large areas of land for a time, most American Indians were split into small tribes that spoke at least 2,000 different languages — ten times the number of languages spoken in Europe. American Indians spoke a lot of languages because they had little reason to conquer and consolidate with neighboring groups. Hunter-gatherers aren't very interested in dominating their neighbors. Only with the beginning of agriculture did property become worth seizing, and people were vulnerable to domination because they couldn't move away from valuable growing crops to avoid being conquered.
Agriculture also fed the large population centers. The Aztecs in Mexico, Mayans in Central America, and Incas in Peru built networks of roads and amazing cities with incredible buildings and artwork. They were experts at raising more than 100 varieties of corn — one kind for every taste and climate. One modern scientific journal calls the American Indians' development of many corn types from a barely edible wild plant the greatest feat of genetic engineering in history.
If the AP test has a question on pre-Columbian American Indians, it may well contain that favorite buzzword of people who write early-history tests: Meso-america. Meso means middle of the New World, as in south Mexico and Central America. This term throws a lot of people because it refers to an area that's not part of the current United States that you thought you were studying.
Questions about advanced southern American Indians may appear on the AP U.S. History test because historians know more about them than they know about the hunter-gatherers and early agriculturalists who peopled what's now the United States. The Mesoamerican culture area included some of the most complex and organized people of the Americas, including the Olmecs, the Mayans, and the Aztecs. These cultures developed advanced political systems; discovered technological, scientific, and mathematical concepts; and participated in long-distance road networks that covered hundreds of miles and resulted in the transmission of ideas and products.