The failure of those negotiations led the Soviet Union to conclude the Molotov-Ribbentrop Pact with Nazi Germany on 23 August; this was a non-aggression pact containing a secret protocol dividing Northern and Eastern Europe into German and Soviet spheres of influence.
One week after the signing of the Molotov-Ribbentrop Pact, German forces invaded Poland from the north, south, and west. Polish forces then withdrew to the southeast where they prepared for a long defence of the Romanian Bridgehead and awaited French and British support and relief they were expecting. The Soviet Red Army invaded the Kresy, in accordance with the secret protocol, on 17 September. The Soviet government announced it was acting to protect the Ukrainians and Belarusians who lived in the eastern part of Poland, because the Polish state had collapsed in the face of the Nazi German attack and could no longer guarantee the security of its own citizens.
On 23 August, 1939, the world was shocked when, suddenly, Russia and Germany signed a 'Non-aggression Pact'.
People would have been even more shocked if they had known at the time that, in addition, the two countries had made a number of a 'secret protocol' agreeing to 'spheres of influence' in Finland, Estonia, Latvia, Lithuania, Romania and Poland. It amounted to an agreement to invade and divide the countries of eastern Europe between them ... with Poland first on the list.
- if he made an alliance with Britain, he would end up fighting a war with Hitler over Poland.
- if he made an alliance with Germany, he would get half of Poland, and time to prepare for the coming war with Germany.
Stalin believed that the pact was a way of keeping the threat posed by Nazi Germany in check. The Soviet Union was in the middle of the last of their five-year plans of rapid industrialization. Stalin knew the words of Mein Kampf; it was no secret that Hitler viewed the destruction of the Soviet Union as his ultimate goal. Stalin is known to have said about the Molotov-Ribbentrop pact that "of course it's all a game to see who can fool whom." The Soviet leader suspected Hitler's Germany would eventually turn on the USSR; what the Soviets needed most was time. However, time was not the only benefit afforded to the Soviet Union by the pact. The Soviet Union gained half of Poland as a further buffer against German attack. With the non-aggression pact signed, Stalin could focus on building his nation and preparing for war.
Beyond the immediate benefits of land and time, Stalin also had his own expectations about the war between imperialist powers that would unfold as a result of this pact. Stalin secretly hoped that the war between France, Britain and Germany, would weaken and possibly destroy some of Communism's mortal enemies. Stalin viewed the democracies with as much contempt as he did Nazi Germany. As a witness to the enormous destruction wrought by World War I, Stalin had every reason to believe that Europe would bleed itself dry again and that, this time, the communist revolutions that had threatened before could succeed with the material aid of the Soviet Union. Stalin could not have asked for much more from the pact, at least in his mind at the time, than the mutual destruction of his ideological foes without risking a single Soviet citizen in war. Reality proved less generous.