Sunni Arab militants from the al Qaeda splinter group known as the Islamic State of Iraq and Syria, or ISIS (also known as the Islamic State of Iraq and the Levant, or ISIL), have gained control of vast tracts of land along the Tigris and Euphrates Rivers in Iraq, and are pushing south toward Baghdad. It’s all part of a wider aim to establish an Islamic caliphate in Syria and Iraq and—eventually—farther away in Asia and Africa. Over the centuries, however, the region once known as the cradle of civilization has seen significant changes. A seventh-century split within Islam itself between Sunni and Shiite would only grow wider as the centuries wore on and the region known as Iraq was traded between great powers.