as jonathan mann reports, the ending was low key compared to the start one march in 2003. >> reporter: what we began with panetta presided over the symbolic ceremony. >> you will leave with great pride, lasting pride, secure in knowing that your sacrifice has helped the iraqi people begin a new chapter in history. >> reporter: more than 4,500 americans have been killed since the conflict began while its estimated that more than 100,000 iraqis have died. >> we look back at the sacrifices made by so many americans and so many iraqis, but we also look forward to an iraq that is sovereign, secure and self-reliant. >> reporter: but nearly nine years after the war began, some current and former u.s. military brass questioned if u.s. troops are leaving too soon. >> in my judgment we could have used the next few years training and developing the iraqi security forces so that those hard one gains that our soldiers have achieved would be permanent and not speculative. >> reporter: of the 5,500 troops still in iraq almost all must leave the country by december 31st. jonathan mann, reporting. >>>

as jonathan mann reports, the ending was low key compared to the start one march in 2003. >> reporter: what we began with shock and awe, and toppled the regime of saddam hussein has now ended quietly with the casing of the colors. the u.s. officially ended its mission in iraq. on thursday u.s. troops in baghdad lowered the american flag for the last time. u.s. defense secretary leon panetta presided over the symbolic ceremony. >> you will leave with great pride, lasting pride, secure in knowing that your sacrifice has helped the iraqi people begin a new chapter in history. >> reporter: more than 4,500 americans have been killed since the conflict began while its estimated that more than 100,000 iraqis have died. >> we look back at the sacrifices made by so many americans and so many iraqis, but we also look forward to an iraq that is sovereign, secure and self-reliant. >> reporter: but nearly nine years after the war began, some current and former u.s. military brass questioned if u.s. troops are leaving too soon. >> in my judgment we could have used the next few years training and de