Whether you realize it or not, this is a very Eurocentric question. Unlike the tech tree mechanics of games like the Civilization series, societal development is not linear nor is the “advanceness” of societies determined by their technological resources. The lack of horses in the Americas did not prevent complex cultures from developing or leaving their mark on history. Sites like Cahokia, Tenochtitlan, Machu Picchu are all impressive in their own way, and they all existed without horses. However, architectural feats alone are not necessary to indicate complexity in societies as one can look at the Iroquois confederacy and their organization. Their confederation was not an insignificant achievement. It is impossible to truly explore all aspects of Native American culture because each tribe can be as different from each other as they were to Europeans.

When horses were introduced into the Americas by the Spanish, they radically changed native culture. Changed, not advanced, is the key word here as “advanced” implies that native societies were inferior to European cultures. Many tribes readily adopted the animals into their societies, but it often came at a cost. Where the Shoshone culture was once agrarian, the horse transformed their society into one of raiding. Other cultures like the Blackfoot found themselves in far more conflict with their neighbors as the horse gave them, and their neighbors, unrivaled ability to control more territory. The list goes on but the story is largely the same: the horse changed their world for better or worse. Some societies completely abandoned their pre-Columbian traditions while others adapted or held on. Their societies were just as complex before and after the horse. If you are interested in pursuing the topic further, I highly recommend you focus on a single tribe or subset of tribes to understand how the horse affected their cultures. Wendell Oswalt’s This Land Was Theirs is another option if you are looking for a briefer look at the cultures of select tribes.