The most accepted theory about the origin of the American Indians is that they managed to come to the Americas at the dying phases of the last Ice Age, so 12-13 thousand years ago. They are thought to have come from Asia, through the Baring Bridge, and moved in the interior of the Americas through the gap in between the two large ice masses on the east and west. This theory has been debated though, both about the origin of the American Indians, and about the timing of their arrival, as there have been found multiple clues that suggest that people from Oceania also migrated toward the Americas through the Pacific, as well as migrating much earlier, almost ten times the time suggested.
The civilization that developed in the Americas were heavily dependent on the living conditions. In North America, there were not lot of great civilizations, and the ones that were, were simple agriculture civilizations, which are known for building mounds for several purposes. In Central America and South America, the conditions were more favorable for more developed civilizations to develop. Apart from being based around agriculture, these civilizations were also building large and beautiful buildings. They perfected the usage of several metals, constructed irrigation and drainage systems, and even converted the land in accordance tot heir needs. The organization was also on a much higher level in Central and South America than in North America.
