U.S. soldiers celebrate as the first vehicles of the last U.S. military convoy carrying troops out of Iraq passes through the K-Crossing at Iraq's border with Kuwait early on Sunday morning. Martin Bureau/AFP/Getty Images hide caption

itoggle caption Martin Bureau/AFP/Getty Images

Iraqi President Jalal Talabani speaks at the opening of the huge U.S. Embassy in Baghdad on Jan. 5, 2009. It is the largest U.S. Embassy in the world. Handout/Getty Images hide caption

itoggle caption Handout/Getty Images

Makeshift houses in Baghdad are the only homes some internally displaced Iraqis know. Many are too afraid to go back to their original homes; for them, the threat of being targeted is still very real. Mohammed Ameen/Reuters /Landov hide caption

itoggle caption Mohammed Ameen/Reuters /Landov

Gen. David Petraeus (center, with no gun) walks with troops in 2007 in Baqouba, Iraq. The area had recently been seized back from al-Qaida control with help from U.S. forces who were part of the surge. The surge is widely credited with changing the course of the war; now, some experts are debating how much credit it deserves. Chris Hondros/Getty Images hide caption

itoggle caption Chris Hondros/Getty Images

A U.S. convoy departs from Contingency Operating Station Kalsu, a U.S. base about 60 miles south of Baghdad. For many U.S. troops, it is the last stop in Iraq on the way out of the country. Sean Carberry/NPR hide caption

itoggle caption Sean Carberry/NPR

The American flag, Iraqi flag, and the U.S. Forces Iraq colors are carried during ceremonies in Baghdad today marking the end of the U.S. military mission in Iraq. Pablo Martinez Monsivais/pool/AP hide caption

itoggle caption Pablo Martinez Monsivais/pool/AP

Iraqi Prime Minister Nouri al-Maliki (left) shakes hands with Iran's President Mahmoud Ahmadinejad during an official meeting in Tehran last year. STR/AFP/Getty Images hide caption

itoggle caption STR/AFP/Getty Images

U.S. Army Lt. Adam Wilson from Ontario, Calif., shakes hands with Sheik Mahmood Al-Ghizzi, possibly for the last time, on Dec. 5 in Nasiriyah, Iraq. The two men met for a final lunch as the U.S. military prepares to leave Iraq after a nearly nine-year presence. Joe Raedle/Getty Images hide caption

itoggle caption Joe Raedle/Getty Images

U.S. troops topple a statue of Saddam Hussein on April 9, 2003, the 21st day of Operation Iraqi Freedom, in central Baghdad. Gilles Bassignac/Gamma-Rapho/Getty Images hide caption

itoggle caption Gilles Bassignac/Gamma-Rapho/Getty Images

Iraqi soldiers take part in a graduation parade in Kirkuk on Monday. The oil-rich city is a mix of Kurds, Arabs, Turkmen and others. Its future status is a source of tension within Iraq. Marwan Ibrahim/AFP/Getty Images hide caption

itoggle caption Marwan Ibrahim/AFP/Getty Images

Vice President Joe Biden is interviewed by NPR's Robert Siegel in the Secretary of War Suite of the Eisenhower Executive Office Building, Dec. 13. David Lienemann/The White House hide caption

itoggle caption David Lienemann/The White House

A day after leaving Iraq last week, U.S. Army soldiers from the 1st Cavalry Division lined up their armored vehicles near Kuwait City, Kuwait. Armored equipment will not stay behind after troops leave Iraq, but other property may. Joe Raedle/Getty Images hide caption

itoggle caption Joe Raedle/Getty Images