That one of the greatest victories of World War II was a mass evacuation — more than 300,000 British and French troops taken off a beach at Dunkirk — was a preview of the industrial nature of that conflict. Feats of organization — such as the return of Allied troops to other French beaches on D-Day — took precedence over military panache. It is the reason that Dwight Eisenhower was the indispensable irreplaceable man, not George Patton.

But Dunkirk also proved the comparative advantage that democracies have in modern war: the ability of free people to self-organize. It was nearly 900 private watercraft, including pleasure boats and paddle steamers, that braved the Luftwaffe to ferry the surrounded troops home. The future of a free Britain was delivered directly by its own citizens.

Christopher Nolan’s film “Dunkirk” is a spare telling of that story from the firsthand perspective of soldiers, sailors, airmen and civilians. Only briefly does the camera pull out to reveal the epic scale of events. Most of the time we are scrambling, flying, swimming and sinking along with the confused participants. There is little dialogue and almost no back story for the main characters. The soldiers are played by essentially interchangeable young actors. But they somehow work as stand-ins for the waiting, vulnerable mass. They are not humanized, just human. And their motivation doesn’t require much artistic development: doing everything they can to get off the damn beach and get home.

The craft of the movie is taking the fragmented individual experiences of the characters and weaving them, inexorably, into a narrative that clarifies in a single scene. I will not sully this review with a spoiler. But the events of the film eventually come together with a pleasing click, dramatizing how the choices of individuals, both noble and base, gather into something larger than themselves. In this case, the deliverance of a nation.

The government leaders of the time have no direct voice in the movie, including the familiar voice of Winston Churchill. The lack of political context works as an artistic device. But the experience of the movie (or so I lectured my children) is enriched by knowing some of the history. The swift collapse of France. The utter isolation of Britain. An American president hamstrung by isolationists, doing what he could to help.

The recognition that World War II was a citizens’ war should not obscure the importance of leadership. Dunkirk, perhaps more than any other event of the war, was Churchill’s moment. As French resistance disintegrated, it was estimated that only 45,000 soldiers could be taken off the beaches before the perimeter collapsed — effectively leaving Britain undefended to German invasion. Churchill told Parliament to prepare for “hard and heavy tidings.” To his War Cabinet he raised the possibility of contaminating British beaches with poisonous gas when the Germans came.

At the same time in the United States, Charles Lindbergh, the original advocate of “America First,” gave a radio address dismissing President Franklin Roosevelt’s proposal for rearmament as “hysterical chatter.” Roosevelt himself told the British ambassador that the British government might need to continue the war from Canada.

In London, Churchill was receiving the same suggestion to move the government and royal family across the Atlantic. He replied that “no such discussion” should be permitted. When the director of the National Gallery proposed sending the most irreplaceable paintings to Canada, Churchill replied, “No, bury them in caves and cellars. None must go. We are going to beat them.”

The tired men of Churchill’s government raised the prospect of a negotiated peace. Churchill responded, “Nations which went down fighting rose again, but those who surrendered tamely were finished.” Speaking to his full cabinet, he said, “If this long island story of ours is to end at last, let it end only when each one of us lies choking in his own blood upon the ground.”

The success at Dunkirk made Churchill’s defiance a realistic option and solidified his hold on power. Guns, ammunition and artillery to rearm the evacuated army flooded in from the Commonwealth and (by clever ruse) from the United States. British planning for a return to the continent began the same month as the Dunkirk evacuation ended. D-Day was already in mind.

It is a brilliant artifice in “Dunkirk” to have Churchill’s most famous oration — “We shall fight on the beaches” — read aloud by one of the soldiers who finally reaches safety. It was ordinary people who gave Churchill’s roar reality and force. But the roar was indispensable.

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