In what way was the outcome obvious to you? The insurgency of the Shias or that of the Sunni's? Be grateful if you could back up your statement with reasoned logic...helpful to all.
Simple really. They had the home side advantage, same as the VC did in the Vietnam Armed Conflict and the emerging US did in the War of Independence and the Jocks against the Romans and the Micks against the British and the French Resistance against the Germans.
What would YOU do if you were faced with an aggressor enemy with superior firepower and tactics? To fight him on his own terms is a strategy destined for failure, but if you disappear amongst your own population, the majority of whom will support you because you are not the outsider you can continue to snipe at will and for every casualty you take there are two two replace them. It's an old story that has been played out many times, so to think that it anything else would happen was naive at best. The war is not over, it's still going on.