The German invasion began one week after the signing of what neutrality pact between Nazi Germany and the Soviet Union signed in Moscow on 23 August 1939?
Invasion of Poland The Invasion of Poland, known in Poland as the September Campaign ("Kampania wrześniowa") or the 1939 Defensive War ("Wojna obronna 1939 roku"), and in Germany as the Poland Campaign ("Polenfeldzug") or "Fall Weiss" ("Case White"), was a joint invasion of Poland by Nazi Germany, the Soviet Union, the Free City of Danzig, and a small Slovak contingent, that marked the beginning of World War II. The German invasion began on 1 September 1939, one week after the signing of the Molotov–Ribbentrop Pact, while the Soviet invasion commenced on 17 September following the Molotov-Tōgō agreement that terminated the Russian and Japanese hostilities in the east on 16 September. The campaign ended on 6 October with Germany and the Soviet Union dividing and annexing the whole of Poland under the terms of the German–Soviet Frontier Treaty.
Oder–Neisse line The Oder–Neisse line (Polish: "granica na Odrze i Nysie Łużyckiej" , German: "Oder-Neiße-Grenze" ) is the international border between Germany and Poland. It was drawn at the Potsdam Conference in the aftermath of the Second World War and is primarily delineated along the Oder and Lusatian Neisse rivers in Central Europe, meeting the Baltic Sea to the north, just west of the Polish seaports of Szczecin and Świnoujście (German: "Stettin" and "Swinemünde"). All prewar German territory east of the line and within the 1937 German boundaries (23.8% of the former Weimar Republic) were placed under International Law Administrative status, with most of it being made part of newly-Communist Poland. The small remainder, consisting of the territory surrounding the German city of Königsberg (now renamed Kaliningrad, in honour of Soviet head of state Mikhail Kalinin) in northern East Prussia, was allocated to the Soviet Union (as Kaliningrad Oblast of the Russian SFSR, today the Russian Federation) after the war (pending the final World War II peace treaty for Germany). The vast majority of the native German population in these territories fled, or were killed or expelled by force. The Oder–Neisse line marked the border between the German Democratic Republic (East Germany) and Poland from 1950 to 1990. East Germany confirmed the border with Poland in 1950, while West Germany, after a period of refusal, finally accepted the border (with reservations) in 1970. In 1990 the newly reunified Germany and the Republic of Poland signed a treaty recognizing it as their border.