Why did 0bama keep us in a war for almost 2 years more than it needed to be?

Why? Iraq should have never started to begin with. It was all based on lies. When its a big lie like Libs and Cons alike have been saying for years now then why did 0bama keep it going so long. He could of stopped it the first week in office. Yes for the Prez its very easy. Look how easy it was for GW to start it. Why didn't 0bama stop it. Now he wants to leave 50,000 security troops still there? Why? The war is and has always been a lie. There is no need.