On this day, 79 years ago, Poland was invaded by the Soviet Union following a secret deal between Stalin and Hitler

German and Soviet officers shaking hands following the invasion. Public Domain

Between 03.00 and 06.00 on the morning of September 17, the Red Army rolled into Poland without officially declaring war with over 4,000 tanks, 3,300 aircraft and 620,000 troops, thereby breaking the non-aggression pact between Poland and the Soviet Union.

Already fighting alone against Germany since September 1, Poland now had no chance of success.

Soviet foreign minister Vyacheslav Molotov declared that Poland had ceased to exist and put into motion the secret protocol contained in the Molotov-Ribbentrop pact under which Poland would be carved up by the two superpowers in what many have called the fourth partition. 

The reason that the Soviets gave for the invasion was that they had to come to the aid of their ‘blood brothers’, the Ukrainians and Belarusians, who were trapped in territory that the Soviets said had been illegally annexed by Poland 20 years before.  

Poland was now in a war it had no possibility of winning, trapped between two behemoths. 

Polish POWs captured by the Red Army during the Soviet Invasion of 1939.Public Domain

Its forces were overwhelmed by the mechanized modern German army, and Poland had nothing left with which to fight the Soviets, it’s 1,400 km border only being defended by poorly armed border guards.

Poland was completely surprised by the Red Army’s invasion. German forces had been pushing from the north, west and south since September 1, Warsaw was under siege, and the Poles were using territory in the east of the country to regroup. 

The disorientation among Polish forces was deepened by Commander-in-Chief Edward Rydz- Śmygły’s order to not fight the Soviets and to only engage if attacked directly. 

This meant that most commanders had to decide for themselves what to do, making a coordinated defence of eastern Poland impossible. 

Meanwhile, the Polish president Ignacy Mościcki, upon learning of the Soviet invasion, ordered the government, the diplomatic corps and all forces to cross the border into Romania, from where they were to make their way to France to carry on the fight against the Germans.

Although many Polish units put up a spirited defence, they had no chance against the two invaders, especially as they were cooperating in many places. For example, the Poles were forced to surrender Lwów on 22 September a few days after the Germans had handed over the siege of the city to the Soviets. 

Soviet invasion of Poland, 1939. Advance of the Red Army troops.Public Domain

When fighting had almost finished, Molotov reported to the Supreme Soviet: “A short blow by the German army, and subsequently by the Red Army, was enough for nothing to be left of this bastard of the Treaty of Versailles”.   

On September 28, the Soviet Union and Germany signed the German-Soviet Treaty of Friendship, Cooperation and Demarcation, which made some alterations to the dividing line agreed between Hitler and Stalin, which had been based on the Curzon line proposed by the British after the First World War. 

When the Soviets drew the borders of Eastern Europe after the war, the line from 1939, with some changes, would constitute Poland’s eastern border as we know it today.

As a result of the agreement with the Germans, the USSR grabbed over 190,000 square kilometres of land with a population of around 13 million. 

The two years following the annexation up to the German invasion of the USSR in Operation Barbarossa saw an intense process of sovietisation and large-scale repressions against Poles who were believed to a possible threat to the new order, which meant most Poles. 

In these two years, around 100,000 Poles were arrested and many were tortured and murdered by the NKVD. 

As many as 1,000,000 were deported to Siberia, a high proportion of whom died. 

The most notable massacre carried out by the Soviets in this period was the murder of around 22,000 Polish military officers, police and intelligentsia in Katyn, Kharkiv and Mednoye near Smolensk.