AP Photo

Seventy years ago this summer, in June of 1940, an aging British politician, who for the previous twenty years had seemed to his countrymen to be one of those entertaining, eccentric, essentially literary figures littering the margins of political life, got up to make a speech in the House of Commons. The British Expeditionary Forces had just been evacuated from France, fleeing a conquering German Army—evacuated successfully, but, as the speaker said, wars aren’t won that way—and Britain itself seemed sure to be invaded, and soon. Many of the most powerful people in his own party believed it was time to settle for the best deal you could get from the Germans.

At that moment when all seemed lost, something was found, as Winston Churchill...