History.com: How Mesopotamia Became the Cradle of Civilization

Environmental factors helped agriculture, architecture and eventually a social order emerge for the first time in ancient Mesopotamia. Mesopotamia's name comes from the ancient Greek word for "the land between the rivers." That's a reference to the Tigris and Euphrates rivers, the twin sources of water for a region that lies mostly within the borders of modern-day Iraq, but also included parts of Syria, Turkey and Iran. The presence of those rivers had a lot to do with why Mesopotamia developed complex societies and innovations such as writing, elaborate architecture and government bureaucracies.