For all that I've tried once or twice, I've never quite managed to figure out what the 1st World War was all about. Something about balance of powers, or retraining German militarism, or something. Yet this vagueness is as nothing when compared to what was probably the third worst war in the 20th century, and by far the worst since the 2nd World War: the war in Congo. Perhaps five million people perished, the killing never really ended, and yet the international community, the UN, the world's media, and everyone else, basically didn't notice; in the rare cases when they did, no-one ever tried seriously to explain what was going on.
Now there's a book which tries to explain, Dancing in the Glory of Monsters: The Collapse of the Congo and the Great War of Africa, by Jason Stearns. The Economist reviews it approvingly here. I don't know if everyone interested in world politics needs to read it, but I can't think why not.