As the world marks the 70th anniversary of the end of European conflict in World War II, Thomas Donlan of Barron’s turns his attention to events that took place five years earlier.

In a season of many anniversaries, May and June hold one that nobody celebrates. Seventy-five years ago, the “phony war” ended with enormous defeats for the British and the French.

Despite their treaty obligation to assist Poland in the event of German attack, despite overwhelming numerical superiority of 110 French and British divisions facing 23 German divisions in the west, the political and military leaders of Britain and France had taken no action in September 1939. They had watched the German army crush Poland while lifting not a finger to back up their declaration of war on Sept. 3. For the next seven months they sat, hoping that it was all a ghastly misunderstanding.

In a way, it was, but the misunderstanding was all theirs. The British and French had learned the wrong lessons from what was then called the Great War, which had started 25 years earlier. The French prepared for defense, rather than attack, but did not prepare adequately for an attack routed through Belgium, like the one the German army had used in 1914. The British, inventors of the tank, were unprepared for a mobile war so unlike the trench warfare of the previous conflict.

Neither the British nor the French undertook significant attacks on land or in the air while the Germans were busy in Poland. They did not even bomb German military targets near the border (although the British did drop 11 tons of propaganda leaflets). Rail lines, supply depots, and airfields went unscathed, ready for the next phase of the war.

France and Britain felt secure behind the Maginot Line and across the English Channel. In April, Prime Minister Neville Chamberlain wrote his sister, “The accumulation of evidence that an attack is imminent is formidable…and yet I cannot convince myself that it is coming.”

The attack came only a few days later, with the German conquest of Denmark and most of Norway, a defeat amplified by a feeble and ill-considered British attempt at a counterattack in the far north of Norway. Chamberlain barely survived a parliamentary vote of confidence after a debate that saw a rebel member quote Oliver Cromwell to the prime minister: “You have sat too long here for any good you have been doing! Depart, I say, and let us have done with you! In the name of God, go!”