In the opening scene of the most famous Polish movie of the past two decades, a crowd of anxious, desperate people—on foot, riding bikes, leading horses, carrying bundles—walks onto a bridge. To their immense surprise, they see another group of anxious, desperate people heading toward them, walking from the opposite direction. “People, what are you doing?!” one man shouts. “Turn back! The Germans are behind us!” But from the other side, someone else shouts, “The Soviets attacked us at dawn!” and both sides keep walking. General confusion ensues.

This scene takes place on September 17, 1939, the day of the Soviet invasion of Poland; the Germans had invaded two and a half weeks earlier. The movie is Katyn. The director, the late Andrzej Wajda, had long wanted to film that scene on a bridge, a visual representation of what happened to the whole country in 1939, when Poland was caught between two invading armies whose dictators had jointly agreed to wipe Poland off the map.

Even while that joint invasion was unfolding, both dictators were already lying about it. The agreement to create a new German-Soviet border in the middle of Poland, as well as to consign Lithuania, Latvia, Estonia, and Finland to a “Soviet sphere of interest,” was part of a secret protocol to the Molotov-Ribbentrop Pact, the nonaggression deal between Hitler and Stalin signed on August 23. The secret protocol was found in Nazi archives after the war, though the Soviet Union went on denying that it existed for many decades.

Each side also manufactured special lies of its own. The Germans sponsored an entire false-flag operation, involving fake Polish soldiers—SS officers in Polish uniforms—who launched an orchestrated attack on a German radio station and broadcast anti-German messages. American newspaper correspondents were summoned to the scene and shown some corpses, which in fact belonged to prisoners, murdered especially for the occasion. This “crime,” together with a few other staged “attacks,” composed Hitler’s formal excuse for the invasion of Poland. On August 22, he told his generals not to worry about the legality of the operation: “I will provide a propagandistic casus belli. Its credibility doesn’t matter. The victor will not be asked whether he told the truth.”