How civilized were the North American Indians before the arrival of European immigrants?

Indians in North America used to be very powerful. In Mexico, there are two powerful countries, the Aztec Empire and the Mayan Empire. Both empires were in slave society.

As for its civilization, it still can't be explained, and its achievements in astronomy, calendar, mathematics and architecture have even reached the advanced level in modern times. How to build Mayan temples and pyramids has always been a mystery. However, when the colonists arrived in America, they were still in a slave society and their military development was very backward. They only use bows and arrows and javelin as weapons.

On the whole, its social level is equivalent to that of China in the pre-Qin period, but its scientific culture has reached or surpassed that of modern Europe.