Many schools no longer teach history, so it’s no surprise that young people today have to absorb the lessons of World War II through books and movies. Gary Oldman might win a Best Actor Oscar for his extraordinary performance as Winston Churchill in Darkest Hour, which is set in the few weeks in May 1940 between Churchill’s becoming prime minister and the mass evacuation of Dunkirk. But there is another event, a couple of years earlier, that could be cast as a “darkest hour.” It goes by a single word: “Munich.”

In its broad outlines, the story is familiar. In September …