Soviet invasion of Poland
The Soviet invasion of Poland was a military conflict by the Soviet Union without a formal declaration of war. On 17 September 1939, the Soviet Union invaded Poland from the east, 16 days after Nazi Germany invaded Poland from the west. Subsequent military operations lasted for the following 20 days and ended on 6 October 1939 with the two-way division and annexation of the entire territory of the Second Polish Republic by Nazi Germany and the Soviet Union. This division is sometimes called the Fourth Partition of Poland. The Soviet invasion of Poland was indirectly indicated in the "secret protocol" of the Molotov–Ribbentrop Pact signed on 23 August 1939, which divided Poland into "spheres of influence" of the two powers. German and Soviet cooperation in the invasion of Poland has been described as co-belligerence.
The Red Army, which vastly outnumbered the Polish defenders, achieved its targets, encountering only limited resistance. Some 320,000 Poles were made prisoners of war. The campaign of mass persecution in the newly acquired areas began immediately. In November 1939 the Soviet government annexed the entire Polish territory under its control. Some 13.5 million Polish citizens who fell under the military occupation were made Soviet subjects following show elections conducted by the NKVD secret police in an atmosphere of terror, the results of which were used to legitimise the use of force. A Soviet campaign of political murders and other forms of repression, targeting Polish figures of authority such as military officers, police, and priests, began with a wave of arrests and summary executions. The Soviet NKVD sent hundreds of thousands of people from eastern Poland to Siberia and other remote parts of the Soviet Union in four major waves of deportation between 1939 and 1941.
Soviet forces occupied eastern Poland until the summer of 1941 when Germany terminated its earlier pact with the Soviet Union and invaded the Soviet Union under the code name Operation Barbarossa. The area was under German occupation until the Red Army reconquered it in the summer of 1944. An agreement at the Yalta Conference permitted the Soviet Union to annex territories close to the Curzon Line, compensating the Polish People's Republic with the greater southern part of East Prussia and territories east of the Oder–Neisse line. The Soviet Union appended the annexed territories to the Ukrainian, Byelorussian and Lithuanian Soviet Socialist Republics.
Following the end of World War II in Europe, the Soviet Union signed the Polish–Soviet border agreement of August 1945 with the new, internationally recognized Polish Provisional Government of National Unity on 16 August 1945. This agreement recognized the status quo as the new official border between the two countries, with the exception of the region around Białystok and a minor part of Galicia east of the San River around Przemyśl, which were later returned to Poland.
Prelude
In early 1939, several months before the invasion, the Soviet Union began strategic alliance negotiations with the United Kingdom and France against the crash militarization of Nazi Germany under Adolf Hitler.Joseph Stalin pursued the Molotov–Ribbentrop Pact with Adolf Hitler, which was signed on 23 August 1939. This non-aggression pact contained a secret protocol, that drew up the division of Northern and Eastern Europe into German and Soviet spheres of influence in the event of war. One week after the signing of the Molotov–Ribbentrop Pact, German forces invaded Poland from the west, north, and south on 1 September 1939. Polish forces gradually withdrew to the southeast where they prepared for a long defense of the Romanian Bridgehead and awaited the French and British support and relief that they were expecting, but neither the French nor the British came to their rescue. On 17 September 1939 the Soviet Red Army invaded the Kresy regions in accordance with the secret protocol.
At the opening of hostilities several Polish cities including Dubno, Łuck and Włodzimierz Wołyński let the Red Army in peacefully, convinced that it was marching on in order to fight the Germans. General Juliusz Rómmel of the Polish Army issued an unauthorised order to treat them like an ally before it was too late. 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 – according to Soviet propaganda, which perfectly echoed Western sentiment that coined the term "Blitzkrieg" to describe Germany's "lightning war" crushing defeat of Poland after just weeks of battle – and could no longer guarantee the security of its citizens. Facing a second front, the Polish government concluded that the defense of the Romanian Bridgehead was no longer feasible and ordered an emergency evacuation of all uniformed troops to then-neutral Romania.
Poland between the two world wars
The League of Nations and the peace treaties of the 1919 Paris Peace Conference did not, as it had been hoped, help to promote ideas of reconciliation along European ethnic lines. Epidemic nationalism, fierce political resentment in Central Europe where there was strong popular resentment to the War Guilt Clause, and post-colonial chauvinism led to frenzied revanchism and territorial ambitions. Józef Piłsudski sought to expand the Polish borders as far east as possible in an attempt to create a Polish-led federation, capable of countering future imperialist action on the part of Russia or Germany. By 1920 the Bolsheviks had emerged victorious from the Russian Civil War and, de facto acquired exclusive control over the government and the regional administration. After all foreign interventions had been repelled, the Red Army, commanded by Trotsky and Stalin started to advance westward towards the disputed territories intending to encourage Communist movements in Western Europe. The Red Army eventually advanced deep into Ukraine and Belarus, and the embattled Ukrainian People's Republic sought military help from Poland to repel the invasion. The joint Polish-Ukrainian armies initially successfully captured the Ukrainian capital, Kyiv, but eventually had to retreat following a massive counteroffensive by the Red Army, culminating in the Polish–Soviet War of 1920. Following the Polish victory upon the Battle of Warsaw, the Soviets sued for peace and the war ended with an armistice in October 1920. The parties signed a formal peace treaty, the Peace of Riga, on 18 March 1921, dividing the disputed territories between Poland and Soviet Russia. In an action that largely determined the Soviet-Polish border during the interwar period, the Soviets offered the Polish peace delegation territorial concessions in the contested borderland areas, that closely resembled the border between the Russian Empire and the Polish–Lithuanian Commonwealth before the first partition of 1772. In the aftermath of the peace agreement, the Soviet leaders steadily abandoned the idea of international Communist revolution and did not return to the concept for approximately 20 years. The Conference of Ambassadors and the international community recognized Poland's eastern frontiers in 1923.Treaty negotiations
German troops occupied Prague on 15 March 1939. In mid-April, the Soviet Union, Britain and France began trading diplomatic suggestions regarding a political and military agreement to counter potential further German aggression. Poland did not participate in these talks. The tripartite discussions focused on possible guarantees to participating countries should German expansionism continue. The Soviets did not trust the British or the French to honour a collective security agreement, because they had refused to react against the Nationalists during the Spanish Civil War and let the occupation of Czechoslovakia happen without effective opposition. The Soviet Union also suspected that Britain and France would seek to remain on the sidelines during any potential Nazi-Soviet conflict. Robert C. Grogin contends that Stalin, had been "putting out feelers to the Nazis" through his personal emissaries as early as 1936 and desired a mutual understanding with Hitler as a diplomatic solution. The Soviet leader sought nothing short of an ironclad guarantee against losing his sphere of influence, and aspired to create a north–south buffer zone from Finland to Romania, conveniently established in the event of an attack. The Soviets demanded the right to enter these countries in case of a security threat. Talks on military matters, that had begun in mid-August, quickly stalled over the topic of Soviet troop passage through Poland in the event of a German attack. British and French officials pressured the Polish government to agree to the Soviet terms. However, Polish officials bluntly refused to allow Soviet troops to enter Polish territory upon expressing grave concerns that once Red Army troops had set foot on Polish soil, they might decline demands to leave. Thereupon Soviet officials suggested that Poland's objections be ignored and that the tripartite agreements be concluded. The British refused the proposal, fearing that such a move would encourage Poland to establish stronger bilateral relations with Germany.German officials had secretly been forwarding hints towards Soviet channels for months already, alluding that more favourable terms in a political agreement would be offered than Britain and France. The Soviet Union had meanwhile started discussions with Nazi Germany regarding the establishment of an economic agreement while concurrently negotiating with those of the tripartite group. By late July and early August 1939, Soviet and German diplomats had reached a near-complete consensus on the details for a planned economic agreement and addressed the potential for a desirable political accord. On 19 August 1939, German and Soviet officials concluded the 1939 German–Soviet Commercial Agreement, a mutually beneficial economic treaty that envisaged the trade and exchange of Soviet raw materials for German weapons, military technology and civilian machinery. Two days later, the Soviet Union suspended the tripartite military talks. On 24 August, the Soviet Union and Germany signed the political and military arrangements following the trade agreement, in the Molotov–Ribbentrop Pact. This pact included terms of mutual non-aggression and contained secret protocols, that regulated detailed plans for the division of the states of northern and eastern Europe into German and Soviet spheres of influence. The Soviet sphere initially included Latvia, Estonia and Finland. Germany and the Soviet Union would partition Poland. The territories east of the Pisa, Narev, Vistula, and San rivers would fall to the Soviet Union. The pact also provided designs for the Soviet participation in the invasion, that included the opportunity to regain territories ceded to Poland in the Peace of Riga of 1921. The Soviet planners would enlarge the Ukrainian and Belarusian republics to subjugate the entire eastern half of Poland without the threat of disagreement with Adolf Hitler.
One day after the German-Soviet pact had been signed, French and British military delegations urgently requested a meeting with Soviet military negotiator Kliment Voroshilov. On 25 August Voroshilov acknowledged, that "in view of the changed political situation, no useful purpose can be served in continuing the conversation." On the same day, however, Britain and Poland signed the British-Polish Pact of Mutual Assistance, which adjudicated, that Britain commit itself to defend and preserve Poland's sovereignty and independence.