Well for what it's worth the Invasion of Iraq was a giant success. The decade trying to rebuild with an incompetent new government, army, and suicide bombers who wanted to make everyone's life hell, however, was a failure.
Makes me wonder what we did in Japan that was so different and yet so much more successful. During the war people were so fearful of the US in Okinawa that tens of thousands committed mass suicide. Maybe it's because Japan isn't filled with a bunch of groups that hate each other, but at the same time we stopped the Euros from killing each other every 5 minutes. So nation building has worked before. If the military leaders were more competent on a plan to fix things post-war then getting involved wouldn't be such a big deal. But they're not.