War- A Failure of Diplomacy?

I heard the "failure of diplomacy" line yesterday, and it got me thinking. I immediately jumped (mentally) to the standard counter example- Hitler & WWII. Hitler was going to attack and only force was going to stop him. At one point a mere platoon of French soldiers would have meant an instant rebellion of Hitler's generals, but even so, that's still force, albeit a small one. So the argument goes. But I backed up a bit further, to the end of WWI, when the Treaty of Versailles was put into effect. The strong economic sanctions virtually guaranteed financial ruin for all of Germany and paved the way for Hitler and his "master race" drivel. So a more reasonable post-WWI policy toward Germany (i.e. the Marshall Plan) would have prevented the economic ruin and left Hitler as a failed painter that nobody ever heard of.
A second counter example is the Iraqi invasion of Kuwait. Saddam wanted more oil, and only force could stop him. And this is quite true. It's a stronger example than WWII. But backing up further, Saddam gained power in the vacuum after the Brits left, so a better post-colonial (or no-colonial-at-all) policy on the part of the Brits might have allowed a peaceful transition to a stable democracy, with all the historical implications that go along with that. If the US hadn't supported Saddam (and other dictators) throughout the Cold War, things might have been different. But this is where the problem with the "failure of diplomacy" line appears. The law of unintended consequences begins to take effect. If we hadn't supported the dictators, could we have won the cold war? Or having won it anyway, would we have a whole mess of little Cubas all over Latin America and the Middle East? Would that be better than the current situation? How could anyone have predicted the War on Terror back in 1950?
The problem is that those who propound that war is always a failure of diplomacy immediately jump to the conclusion that diplomacy will always be sufficient in practice to prevent war, if we'd just give the diplomats more time. That conclusion is not warranted. In practice, the correct diplomatic move is not at all clear. France could not have known that a single platoon to contest the German militarization of the Rhineland would have prevented the war. It could have just as easily started one, and they had to make a call based on limited information. So they did what they did and the rest is history. And more time for diplomats is more time for rape rooms, concentration camps, murdered Buddhist monks and further military buildup on the part of the aggressor. Sometimes peace costs more than war.
The problem is that people make mistakes. They fail. Failure of diplomacy is a reality. It always will be. It doesn't always lead to war, but sometimes it does. That doesn't mean that the war shouldn't be fought. Life is what it is, and decisions are made now, not a year ago. How a war started isn't nearly as important as how it ends.