What is the leading theory about how early humans arrived on the american continents?

The leading theory is that they came to the Americas during a migration that occurred while the continents of Africa and the Americas were still not divided. They moved there thousands of years before the colonies were even established or before the civilizations rose.

Iraq

Western Asia situated within the Tigris–Euphrates river system, in modern days roughly corresponding to most of Iraq. It also includes parts of Kuwait Saudi Arabia and Syria. Mesopotamia was dominated by the Sumerians and the Akkadians. Mesopotamia is also the site of the earliest developments of the Neolithic Revolution