I just read an excellent book on World War I, and it made me incredibly sad. World War I was the beginning of all the horrors of the 20th century and of problems we still have to deal with in the 21st century. It all started there.
What's so sad is that we really learned nothing – not from World War I, not from World War II, not from Korea or Vietnam or the Cold War. It's almost as if world leaders in every country manage to get through school without learning anything about the past.