A failed Iraq would not just be a second Vietnam, nor would it just be America's problem. It would be a symbolic victory for al-Qaeda, a safe haven for jihadists to plot future September 11s and July 7s, and a battleground for a Shia-Sunni struggle that could draw in the entire Middle East. Our future peace and prosperity depend, in part, on fixing this mess. And, a year ago, few had much hope. To appreciate the scale of the task Gen Petraeus took on, it is necessary to go back to February 22, 2006. Or, as Iraqis now refer to it, their own September 11. That was when Sunni-led terrorists from al-Qaeda blew up the Shia shrine in the city of Samarra, an act of provocation that finally achieved their goal of igniting sectarian civil war.