This 2011 was Bush's agreement and Obama had "O" to do with it. It would have happened with any President...unless there was anew agreement.
Psst...there's still about 20,000 folks left there....a paid by USA security force.
The bare outline.
“The U.S.–Iraq Status of Forces Agreement (official name: “Agreement Between the United States of America and the Republic of Iraq On the Withdrawal of United States Forces from Iraq and the Organization of Their Activities during Their Temporary Presence in Iraq”) was a status of forces agreement (SOFA) between Iraq and the United States. It established that U.S. combat forces would withdraw from Iraqi cities by June 30, 2009, and all U.S. forces will be completely out of Iraq by December 31, 2011.”
“On December 4, 2008 Iraq’s presidential council approved the security pact. “Nothing has been changed (in the accord)”, presidency secretary Nasir al-Ani said after it was reviewed by the body. The council decision marks the final hurdle for the pact in terms of Iraqi government or legislative approval.”
“On December 14, 2008, U.S. President George W. Bush signed the security pact with Iraq.”
Source: Wikipedia