On 17 September 1939, Soviet troops invaded Poland fulfilling the provisions of a secret annex to the Ribbentrop-Molotov Pact, signed by the Third German Reich and the Soviet Union on 23 August 1939. The Soviet-German agreement called for dividing up Poland’s territory between the two totalitarian states. The Soviet Union committed itself to supporting Germany in its military operations against Poland.
The pretext for the Soviet invasion of Poland was the recognition by the Soviet government of the non-existence of the Polish state after Germany’s invasion of Poland and the expectation that the Polish government would leave Warsaw. In doing so, the Soviet authorities had declared the Polish-Soviet Non-Aggression Pact of 1932, a bilateral agreement then in force, to be null and void. In reality, until 17 September, the supreme Polish authorities were still in the country, and President Ignacy Mościcki declared the Soviet operation to be an act of aggression in his address. There is no doubt that these operations were a violation of the Polish-Soviet bilateral agreement and international law.
Soviet troops faced resistance from the Polish side in Wilno, Grodno, Lwow and elsewhere. In these cities, like across all eastern voivodeships of the Second Polish Republic, many acts of Soviet violence took place against Polish POWs and the civilian population. In order to justify that the invasion was done to protect the Belarusian and Ukrainian population, the Soviet authorities openly encouraged representatives of these nationalities to wage attacks on Poles.
With regular Soviet army troops arrived special NKWD units, whose role was to eliminate the Polish state structures and a potential resistance movement. To this end, mass-scale arrests and executions of higher placed members of the society were carried out in the Soviet-occupied territories. The majority of Polish Army officers were taken into captivity by the Soviets and became victims of the Katyn Crime, in violation of war-time customs and conventions. Hundreds of thousands of Poles were deported inside the Soviet Union (mostly to Siberia and Kazakhstan). As the Soviets had repeatedly declared, their operations were ultimately targeted at eliminating the Polish state and incorporating the occupied lands into the Soviet state.
The Soviet invasion of Poland speeded up the Polish government’s decision to leave the country on the night of 17 September 1939. This led to organising state and military structures of the Republic of Poland in Exile headed by President Władysław Raczkiewicz. Continuity of institutions was thus preserved enabling the Polish Armed Forces to carry on fighting abroad.
Poland’s defeat in the defensive war of 1939 did not put an end to fighting at home. In the face of repressions by both occupiers, as early as on 27 September 1939, the Service for the Victory of Poland (Polish: Służba Zwycięstwu Polski) was formed. Clandestine structures of the Polish resistance movement made it possible to create the biggest underground state in Europe. The result of operations by two criminal totalitarian regimes led to the partitioning of Poland, left alone in its struggle. Mass-scale exterminations of the population in the occupied Polish lands followed and were continued until practically the last day of World War Two in 1945.
World War Two was one of the most traumatic periods in Poland’s history. Its consequences continue to exert a major impact on Polish foreign policy. Despite the passage of 79 years since September 1939, the Polish nation continues to play the role of a special guardian of memory about these events. The war that began at daybreak on 1 September 1939 by the Third German Reich’s invasion of the Republic of Poland was the most barbaric and genocidal conflict in the history of the world. It is unparalleled both on account of the tens of millions of its victims, its enormous material losses, but also on account of the complete breakdown of all moral and ethical norms.