Iraq, officially the Republic of Iraq, is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert. Historically, the territory comprising Iraq was known in Europe by the Greek toponym 'Mesopotamia' (Land between the rivers). Iraq has been home to continuous successive civilizations since the 6th millennium BC. The region between the Tigris and Euphrates rivers is identified as the cradle of civilization and the birthplace of writing and the wheel. Throughout its long history, Iraq has been the center of the Akkadian, Assyrian, Babylonian, Hellenistic, Parthian, Sassanid and Abbasid empires, and part of the Achaemenid, Roman, Rashidun, Umayyad, Mongol, Ottoman and British empires.[4][5] The Kingdom of Iraq was founded in 1932. Beginning with an invasion in 2003, Iraq came under military occupation by a multinational coalition of forces, mainly American and British. The occupation ended when sovereignty was transferred to the Iraqi Interim Government June 2004. As of January 2010, 112,000 US troops remain in the country. A new Constitution of Iraq has since been approved by referendum and a new Government of Iraq has been elected. There is a deadline for the withdrawal of U.S. military forces from Iraq by 31 December 2011.