In August 1939, a German plane touched down in Moscow and Soviet officials had to borrow a swastika flag from a film studio to greet Joachim von Ribbentrop. That borrowed flag is the perfect symbol for the Molotov-Ribbentrop Pact, an alliance of pure theater between two regimes whose ideologies demanded the destruction of the other. This episode traces how Nazi Germany and the Soviet Union went from fighting a proxy war in Spain to signing a ten-year non-aggression treaty with a secret protocol that divided Poland, the Baltic states, Finland and Bessarabia into spheres of influence.

We look at the economic logic behind the deal, the Munich Agreement that fed Stalin’s paranoia about the West, the British delegation that arrived in Moscow by slow boat without credentials, and the replacement of Maxim Litvinov with Vyacheslav Molotov as a signal to Berlin. Then we follow the pact through the invasion of Poland, the breakdown over Romanian oil, Operation Barbarossa, and the extraordinary story of the German civil servant who buried microfilm copies of the secret protocol in a tin can, giving the Allies proof at Nuremberg that the Soviets denied for forty years.

• Why the Comintern, the Anti-Comintern Pact and the Spanish Civil War made a German-Soviet deal seem impossible
• How fear of a British blockade and Stalin’s need for industrial machinery created a supply-chain match
• The diplomatic blunders of Britain and France that pushed Stalin toward Hitler
• The secret protocol’s river-line border through Poland and the later trade involving Lithuania
• How Karl von Loesch’s buried microfilm survived, and why those 1939 borders still shape Ukraine, Belarus, Lithuania and Moldova today