I'm reading a fascinating book about the peace conference at the end of World War One called Paris 1919. For a few months, the victors were in Paris: US, UK, France, Italy (until they left in a snit), Japan (when they were listened to), and other little ones. They also had delegations from everyone. Serbs, Zionists, Prince Faisal. Even Ho Chi Minh, who happened to be living in Paris, tried to bring their attention to Vietnam (he was ignored). They had a lot to do, and it's amazing how many things that crossed their collective desks were decided incorrectly. Most conflicts of the last 85 years have their origins at this conference.
World War Two (Europe)--the peace terms imposed on Germany were too harsh
World War Two (Asia)--they managed to turn BOTH China and Japan away from being liberal democracies, so China moved to the left, Japan moved to the right, and their territorial differences were not solved at all
Balkans (1980s, 1990s)-Yugoslavia came into being on its own in 1918 but was endorsed here; even in 1919 the Serbs were arrogent, overbearing jerks
Middle East (1920s-present)--they invented the following countries: Iraq, Syria, Jordan, Israel (effectively), Lebanon. One could argue they did a poor job with every single one of them. They tried to control Egypt and Saudi Arabia also, but events on the ground moved too fast for them. As bad as they screwed up Europe and Asia, this may be their most lasting mistake. After all, most of Yugoslavia is peaceful these days (and plotting to take over the NBA), and that's the only mistake left in Europe. They can't be blamed for ongoing unrest in Asia. But the entire shape of the Middle East was created at this conference (except for Iran, which wasn't their fault). And they did a poor, poor job of it. Iraq, for example, should not exist. It should be three countries. And yet it might still.
That's another interesting feature of what happened. Many of their mistakes were unmade later, but at the cost of millions of lives. Except Czechoslovakia, which was invented here but had the good sense to split peacefully.
All this aside, did they do a bad job? That's sort of another way of asking if anyone else could have done any better. They had a lot of problems. To take perhaps the most obvious example, no one had any idea what was going on in Russia because it was, inconveniently, in the midst of the Bolshevik Revolution. So they were trying to do things like draw boundaries for Poland and Turkey without Russia's input and without knowing whether any government in Russia even existed.
If, like me, you believe that to understand the present one must understand the past, this book is essential reading. I've learned an amazing amount from it and I highly recommend it.