On August 23, 1939–shortly before World War II (1939-45) broke out in Europe–enemies Nazi Germany and the Soviet Union surprised the world by signing the German-Soviet Nonaggression Pact, in which the two countries agreed to take no military action against each other for the next 10 years. With Europe on the brink of another major war, Soviet leader Joseph Stalin (1879-1953) viewed the pact as a way to keep his nation on peaceful terms with Germany, while giving him time to build up the Soviet military. German chancellor Adolf Hitler (1889-1945) used the pact to make sure Germany was able to invade Poland unopposed. The pact also contained a secret agreement in which the Soviets and Germans agreed how they would later divide up Eastern Europe. The German-Soviet Nonaggression Pact fell apart in June 1941, when Nazi forces invaded the Soviet Union.

Germany’s Aggression in Europe Stokes Fears of War

On March 15, 1939, Nazi Germany invaded Czechoslovakia, breaking the agreement it had signed with Great Britain and France the year before in Munich, Germany. The invasion jolted British and French leaders and convinced them that Adolf Hitler, the German chancellor, could not be trusted to honor his agreements and was likely to keep committing aggressions until stopped by force or a massive deterrent.

In the previous year, Hitler had annexed Austria and had taken the Sudetenland region of Czechoslovakia; in March 1939, his tanks rolled into the rest of Czechoslovakia. It appeared that he was determined to undo the international order set up by the Treaty of Versailles, the 1919 peace settlement that ended World War I (1914-18). (The treaty, which required Germany to make numerous concessions and reparations, was highly unpopular with Hitler and his Nazi Party.) It also seemed that Hitler was planning to strike next against its neighbor Poland. To block him, France and Britain pledged on March 31, 1939, to guarantee Poland’s security and independence. The British and French also stepped up diplomatic engagement with the Soviet Union, trying to draw it closer by trade and other agreements to make Hitler see he would also have to face Joseph Stalin if he invaded Poland. But Hitler already knew the Soviets would not stand by if he tried to occupy Poland–an act that would extend the border of Germany right up to the Soviet Union. He also knew France and the Soviets had concluded a defense alliance several years earlier–a treaty that gave Stalin an additional reason to fight Germany if it ventured into Poland and triggered France’s pledge.

It was clear during the tense spring and summer of 1939 that little, if anything, could be taken for granted. In May, Germany and Italy signed a major treaty of alliance, and Hitler’s representatives had begun conducting important trade talks with the Soviets. Just two years prior, however, as Laurence Rees notes in “War of the Century: When Hitler Fought Stalin,” Hitler had called the Soviet Union “the greatest danger for the culture and civilization of mankind which has ever threatened it since the collapse of the … ancient world.”

Hitler and Stalin Rethink their Positions

Through the spring and summer of 1939, Hitler stepped up his demands on the Polish government in Warsaw, and pushed for allowing Germany to reclaim the port city of Danzig (a former German city internationalized by the Treaty of Versailles). Hitler also wanted to put a stop to the alleged mistreatment of Germans living in the western regions of Poland. At the same time, he advanced his plans for attacking Poland in August 1939 if his demands were not met. However, Hitler’s fervor for a war with Poland made his generals nervous. They knew Stalin’s purges of his military commanders in 1937 and 1938 had seriously weakened the Soviet army, but the Germans were leery of a campaign that could easily lead to the nightmare faced in World War I–a two-front war, in which they would be fighting Russians troops in the east and French and British troops in the west.

To avoid such a scenario, Hitler had cautiously begun exploring the possibility of a thaw in relations with Stalin. Several brief diplomatic exchanges in May 1939 fizzled by the next month. But in July, as tensions continued building across Europe and all major powers were feverishly casting about for potential allies, Hitler’s foreign minister dropped hints to Moscow that if Hitler invaded Poland, the Soviet Union might be permitted some Polish territory. This caught Stalin’s attention. On August 20, Hitler sent a personal message to the Soviet premier: War with Poland was imminent. If Hitler sent his foreign minister to Moscow for a vitally important discussion, would Stalin receive him? Stalin said yes.

The Germans and Soviets Make a Deal

On August 22, 1939, German foreign minister Joachim von Ribbentrop (1893-1946) flew from Berlin to Moscow. He was soon inside the Kremlin, face-to-face with Stalin and Soviet foreign minister Vyacheslav Molotov (1890-1986), who had been working with von Ribbentrop to negotiate an agreement. (The Soviet minister is also the namesake for the incendiary device known as a Molotov cocktail.) Ribbentrop carried a proposal from Hitler that both countries commit to a nonaggression pact that would last 100 years. Stalin replied that 10 years would be sufficient. The proposal also stipulated that neither country would aid any third party that attacked either signatory. Finally, the proposal contained a secret protocol specifying the spheres of influence in Eastern Europe both parties would accept after Hitler conquered Poland. The Soviet Union would acquire the eastern half of Poland, along with Lithuania, Estonia and Latvia.

During the Kremlin meeting, Ribbentrop several times telephoned Hitler, who was nervously awaiting news at his country estate in Bavaria. Finally, in the early hours of August 23, Ribbentrop called to say that everything had been settled. As Ian Kershaw notes in “Hitler: 1936–1945: Nemesis,” the German chancellor was ecstatic. He congratulated his foreign minister and said the pact “will hit like a bombshell.” It neutralized the French-Soviet treaty, which would reassure Hitler’s generals, and cleared the way for Germany’s attack on Poland.

Aftermath

The public part of the Moscow agreement was announced with great fanfare on August 25, 1939, the day Hitler had planned to launch his “blitzkrieg” (quick, surprise attacks) strike east into Poland. Earlier this same day, however, Great Britain and France, knowing the Nazi-Soviet agreement was pending, reacted by formalizing their pledge to Poland in a treaty declaring each would fight in Poland’s defense if it were attacked.

Hitler was incensed by this counterthrust but quickly cancelled his order for the invasion. Then, in a wild gamble that France and Great Britain would not meet their treaty obligations to Poland, and knowing he had nothing to fear from the Soviet army, Hitler ordered his troops to strike east into Poland on September 1, 1939. Two days later, on September 3, France and Great Britain declared war on Germany. World War II had begun. And less than two years after that, Hitler scrapped his pact with Stalin and sent some 3 million Nazi soldiers pouring into the Soviet Union on June 22, 1941.

Four years later, with no hope of a German victory in World War II, Hitler committed suicide on April 30, 1945. On May 8, the Allies accepted Nazi Germany’s surrender.