The US exit from Iraq was a humiliation for the world's biggest superpower. Barack Obama wanted to fulfil his commitment to pull out of Iraq by 31 December 2011, but he also wanted to leave some troops in place. He didn't get his way. The Iraqi authorities refused to extend an agreement of immunity from prosecution for US troops beyond 2011 - so Obama had to pull them all out.
Obama once described Iraq as the "dumb war", yet in his speech to soldiers in the US marking the pull out he called it "an extraordinary achievement".