Straddling the Tigris and Euphrates rivers and once known as Mesopotamia, Iraq was the site of flourishing ancient civilizations. Arabs invaded the region in the 7th century and brought the Muslim religion, and for a time Iraq was the heartland of the Islamic Empire. The 13th century Mongol invasion followed by Ottoman Turks, and Iraq became part of Ottoman Empire from the 15th century. It came under British control after World War I, and gained independence in 1932. After a military coup that overthrew the monarchy, Iraq was declared a republic in 1958. Territorial disputes with Iran led to a costly eight-year war (1980-88). In August 1990, Iraq seized Kuwait but was expelled by U.S.-led, UN coalition forces during the Gulf War in early 1991. Following Kuwait's liberation, the UN Security Council required Iraq to surrender all weapons of mass destruction and long-range missiles and to allow UN verification inspections. Continued Iraqi noncompliance with UNSC resolutions over a period of 12 years led to the US-led invasion of Iraq in March 2003 and the ouster of the Saddam Hussein regime. In October 2005, Iraqis approved a constitution in a national referendum and elected a Council of Representatives (CoR) in December 2005. The CoR approved most cabinet ministers in May 2006, marking the transition to a constitutional government. Iraq’s economy is dominated by the oil sector. The country has the world’s third-largest oil reserves and considerable gas reserves. Although it has improved considerably, the security situation remains volatile in Iraq.