Was the war a mistake?

I just spent 2 hours reading in my American History book about the causes of World War II. The book went on and on about how much of a mistake it was for America not to do something about dictators in Europe and Asia before the war started. It's so strange that Americans and other democracies were SO scared of getting into conflict with the dictators of the world at that time. It's simple to us looking back that those were evil things that Hitler and other dictators were doing yet America wanted to stay isolated as long as they could to keep tax dollars down because of the depression.
It makes me think about how people react to the war now. If we didn't intervene 5 years ago would there be a bigger mess? Or did we handle the situation completely wrong? There's no way to know that for sure. I'm tired of that always coming up in the debate over whether to stay in Iraq or not. There's no way to know if we SHOULD have gone to war. We DID go to war and that's the situation. It's frustrating that the presidential candidates are so stuck on that. We need to figure out the best way possible to get out of there in time. I don't want lives that were already lost to be lost in vein but I don't want anymore to be lost at all. I guess it's just a fact of war but there needs to be a good solution and all solutions I've heard so far aren't good enough. Politics seem to get in the way of smart decisions sometimes.