US President George W. Bush began a farewell to Iraq Sunday, the country he ordered invaded in 2003, according to the White House. The White House said Bush had come to meet Iraqi leaders, thank the troops and celebrate a new security agreement. This is Bush's fourth visit to Iraq since US-led troops toppled the regime of president Saddam Hussein in April 2003. The visit comes after Iraq approved a status of forces agreement with the United States, which calls for the withdrawal of all US troops by the end of 2011.