Winning the peace

One of the key arguments of those who say we can't go it alone is that we will need the support of many countries to "win the peace." Everyone acknowledges that, with a few exceptions for convenience sake, the US doesn't really need anyone's help to win the actual war (we already have more US soldiers in the guld than are in the entire British Army, for example)--though it'd be nice. But winning the peace will be a long struggle that allies could surely play a useful role in. But here is the point: what country would refuse to aid in the rebuilding of post-war Iraq simply because they didn't pre-approve the war? It seems to me that there are a myriad of examples of the UN and countries all around the world who step in to help in war torn countries rebuild even though they didn't support the war. In fact, this seems to be the rule, not the exception. So this idea that we need allies to win the peace just doesn't seem rational--we may need them, but we'll get them.