A breakthrough in the German preparations for the war with Poland was the non-aggression pact with the Soviet Union signed on 23 August 1939. According to a secret protocol accompanying the pact, the establishment of a German–Russian border was planned along the rivers Narew, Vistula, and San. Soviet authorities, alarmed by rapid progress of the German army, finally decided to enter Polish territory on 17 September at 4 (6 a.m. Moscow time) in the morning (three hours earlier, the decision was communicated to Wacław Grzybowski, the Polish ambassador in Moscow), justifying that step – according to an interpretation published in Pravda – with the need to provide care for Belarusians and Ukrainians, who were ethnic minorities persecuted inpre-war Poland.
Within two weeks of the campaign, Soviet troops invaded an enormous area – 200,000 square kilometres – of Eastern Poland. The Polish army, following the directive of the commander-in-chief Marshal Edward RydzŚmigły, barely resisted the new aggressor. Furthermore, with only 11,000 soldiers, the Border Protection Corps (Korpus Ochrony Pogranicza) troopscommanded by General Wilhelm Orlik-Rückemann were unable to fight back the Soviet forces of nearly half a million soldiers. In total, the Russian losses in the war of September 1939 amounted to 737 killed and 1,862 wounded accord-ing to the official data; modern historians estimate the numbers as between 2,500–3,500 killed and 8,000–10,000 thousand wounded; Polish losses were much higher.
The final shape of the German–Soviet demarcation line was established by the German-Russian Frontier Treaty, signed in Moscow on 28 September 1939. According to the treaty, the border ran along the rivers of Pisa, Narew, Bug, and San. In exchange for additional Polish territories, the Germans supported Russian aspirations in the Baltic States. On 31 October, during the session of the Supreme Council, Soviet Commissar for Foreign Affairs Vyacheslav Molotov praised the German–Soviet joint action, as a result of which Poland – “a bastard of the Versailles Treaty” – was destroyed with a single blow. The Soviet Union ultimately took 201,000 square kilometres (51.6 per cent of the pre-war Polish territory), inhabited by more than 13 million people (37.3 per cent), including nearly 5.5 million Poles, 1.3 million Jews, 4.7 million Ukrainians, and 1.5 million Belarusians. When dividing the Polish lands, theoccupiers recognised Lithuanian claims to the so-called Central Lithuania.
GENERA L INTRO D U C TION XXIV
