Which three nations did the Tigris and Euphrates rivers flow

Turkey, Syria, and Iraq

The rivers "Tigris and Euphrates" flow through three nations Eastern Turkey, Syria, Iraq.

Explanation:

The rivers Tigris and Euphrates form the major river system in "Western Asia". The two rivers originating in Eastern Turkey in the "mountains of Eastern Anatolia", descend through valleys to the lands of "Syria and Northern Iraq". This leads to the "alluvial plains of central Iraq". The rivers through the central plains combine and get into the "Persian Gulf". The ecoregion with two rivers is described as the 'Cradle of Civilization' known to be the first emerged civilization.