World War I is still being fought a century later, if you recognize the Israel-Palestine conflict (and the attendant rise of Islamist extremism) as outgrowths of that war’s unsatisfactory conclusion. The idea isn’t new but Robert Gerwarth, history professor at University College Dublin, labors to find a new twist in The Vanquished. The title alludes to his thesis that a culture of bitterness, in nations that felt defeated by the war, led to catastrophic upheavals in Europe and the Near East. Gerwarth tries to diminish the theory by UW-Madison’s George Mosse that the war’s extreme brutality damaged many participants and led to berserker violence by Nazis, Fascists and Bolsheviks. He offers instead that many veterans were unable “to leave the war behind them.” As in any investigation of large-scale events, many causes can be discerned. Theory aside, Gerwarth writes with enviable clarity of the post-peace conflagrations that engulfed much of the world and provides a panoramic overview instead of the usual nation-by-nation accounts.