In London, Churchill boarded a train along with leaders of the major parties, ready for a rendezvous with destiny. The train would travel to the coast, and then the party would sail by ship to meet the French government and sign the Act of Union.

The train never left the station. The scheme collapsed as quickly as it arose. In the days prior to June 16, the French government had become consumed by defeatism, as well as anger at Britain for the perceived abandonment at Dunkirk (over 100,000 French troops had been rescued but thousands more were left behind on the beach, where they were forced to surrender to the Germans). Reynaud presented the proposal to the French Council of Ministers, but it was rejected as a British plot to seize the French empire. Marshal Pétain, 84 years old and the great hero of World War I, believed it was his duty to save France from total destruction and accept an armistice with Germany. Britain was doomed, he said, and union would be “fusion with a corpse.” Another minister concluded: “Better be a Nazi province. At least we know what that means.” Reynaud later wrote in his memoirs, “Those who rose in indignation at the idea of union with our ally were the same individuals who were getting ready to bow and scrape to Hitler.”

After hearing news of the French decision, Churchill left the train “with a heavy heart.” He drove to Downing Street and got back to work. Within days, Pétain took over the French government and pursued an armistice with Germany. Britain was alone.

The Franco-British Union is an extraordinary near-miss of history. Defeatism struck the French government late but decisively. If Reynaud had proposed the idea a week, or even a few days, earlier, it might well have been accepted. And we can only guess at the consequences. The French might have kept fighting from their empire, with no Vichy regime. Britain and France might have extended the offer of union to other exiled governments like Poland, Czechoslovakia, Belgium, or Holland—and created a United States of Europe. The war could have ended with three great powers: the USA, the Soviet Union, and the USE.

In the collapse of the Franco-British Union, we can discover the seeds of the European integration project. One of the civil servants who crafted the plan in 1940 was Jean Monnet, who would later become an architect of integration and be known as the “father of Europe.” Monnet said, “Ideas do not die and if nations can come so close together in war, perhaps we can carry some fraction of that accord into the peace.” The lesson that struck Monnet and other federalists with such force in 1940 would become even stronger after 1945. Only European integration could overcome the catastrophe of nationalism and militarism, which delivered two world wars in a generation. And the story of the Franco-British Union also reveals another powerful reason for integration: threat. In 1940, the German menace convinced ardent nationalists like Churchill and de Gaulle to back the union idea. After 1945, the Soviet peril was a driving force behind the European project.