It comes as a surprise to a British reader to find World War I routinely referred to, by Americans, as America’s “forgotten war.” The British would never use such a term. It is true that certain significant aspects of the war have faded from the collective memory. Every one of us can remember why World War II was fought (“Hitler had to be stopped”), but few can do the same for World War I. Yes, the archduke had been shot in Sarajevo, but who the archduke was, and why his assassination led to general war, and why the war was or wasn’t worth fighting—that takes a rarer expertise to answer.