The country that is now Iraq occupies a large part of the region once known as Mesopotamia, which has hosted numerous cultures over the centuries. Human civilizations, including the Sumerian, Babylonian, Assyrian and Parthian cultures flourished in the land between the Tigris and Euphrates rivers since 3,000 B.C. In the seventh century Islam spread quickly in the region, and in the eighth century the Abbasid family established a caliphate with Baghdad as its capital.
The Mongols, with Genghis Khan as their leader, conquered Baghdad in the 13th century and razed the city. Mesopotamia fell to the Ottoman Empire in the 16th century, and remained under Ottoman rule until the British invaded modern-day Iraq in World War I.