Question: 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?

 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 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 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. <SEP> The Molotov–Ribbentrop Pact, also known as the Nazi–Soviet Pact, the German–Soviet Non-aggression Pact or the Nazi German-Soviet Pact of Aggression (officially: "Treaty of Non-aggression between Germany and the Union of Soviet Socialist Republics"), was a neutrality pact between Nazi Germany and the Soviet Union signed in Moscow on 23 August 1939 by foreign ministers Joachim von Ribbentrop and Vyacheslav Molotov, respectively.  The pact was followed by the German-Soviet Commercial Agreement in February 1940. <SEP> The German-Soviet Frontier Treaty was a second supplementary protocol, of the 1939 Hitler-Stalin Pact (known as the "German-Soviet Treaty of Nonaggression", or by its original name of the "German–Soviet Treaty of Friendship, Cooperation and Demarcation").  It was a secret clause as amended on September 28, 1939 by Nazi Germany and the Soviet Union after their joint invasion and occupation of sovereign Poland.  It was signed by Joachim von Ribbentrop and Vyacheslav Molotov, the foreign ministers of Germany and the Soviet Union respectively, in the presence of Joseph Stalin.  The treaty was a follow-up to the first secret protocol of the Molotov–Ribbentrop Pact signed on August 23, 1939 between the two countries prior to their invasion of Poland and the start of World War II in Europe.  Only a small portion of the protocol which superseded the first treaty was publicly announced while the spheres of influence of Nazi Germany and the Soviet Union remained classified.  The third secret protocol of the Pact was signed on January 10, 1941 by Friedrich Werner von Schulenberg, and Molotov, whereas Germany renounced its claims to portions of Lithuania, only a few months before their anti-Soviet Operation Barbarossa. <SEP> The Soviet–Japanese Neutrality Pact (日ソ中立条約 , Nisso Chūritsu Jōyaku ) , also known as the Japanese–Soviet Non-aggression Pact (日ソ不可侵条約 , Nisso Fukashin Jōyaku ) , was a pact between the Soviet Union and the Empire of Japan signed on April 13, 1941, two years after the brief Soviet–Japanese Border War (1939).  The pact was signed to ensure the neutrality between the Soviet Union and the Empire of Japan during World War II, in which both countries participated.