


The success of the invasion marked the end of the Second Polish Republic, though Poland never formally surrendered. On 6 October, following the Polish defeat at the Battle of Kock, German and Soviet forces gained full control over Poland. Facing a second front, the Polish government concluded the defence of the Romanian Bridgehead was no longer feasible and ordered an emergency evacuation of all troops to neutral Romania. On 17 September, the Soviet Red Army invaded Eastern Poland, the territory beyond the Curzon Line that fell into the Soviet " sphere of influence" according to the secret protocol of the Molotov–Ribbentrop Pact this rendered the Polish plan of defence obsolete. France invaded a small part of Germany in the Saar Offensive, and the Polish army was effectively defeated even before the British Expeditionary Force could be transported to Europe, with the bulk of the BEF in France by the end of September. On 3 September, based on their alliance agreements with Poland, the United Kingdom and France declared war on Germany in the end their aid to Poland was very limited. Polish forces then withdrew to the southeast where they prepared for a long defence of the Romanian Bridgehead and awaited expected support and relief from France and the United Kingdom. After the mid-September Polish defeat in the Battle of the Bzura, the Germans gained an undisputed advantage. As the Wehrmacht advanced, Polish forces withdrew from their forward bases of operation close to the Germany–Poland border to more established defense lines to the east. Slovak military forces advanced alongside the Germans in northern Slovakia. German forces invaded Poland from the north, south, and west the morning after the Gleiwitz incident. The invasion is also known in Poland as the September campaign ( Polish: kampania wrześniowa) or 1939 defensive war (Polish: wojna obronna 1939 roku) and known in Germany as the Poland campaign ( German: Überfall auf Polen, Polenfeldzug).

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. The Soviets invaded Poland on 17 September. The German invasion began on 1 September 1939, one week after the signing of the Molotov–Ribbentrop Pact between Germany and the Soviet Union, and one day after the Supreme Soviet of the Soviet Union had approved the pact. The Invasion of Poland, also known as the September Campaign, Polish Campaign, War of Poland of 1939, and Polish Defencive War of 1939 (1 September – 6 October 1939), was a joint attack on the Republic of Poland by Nazi Germany, the Slovak Republic, and the Soviet Union which marked the beginning of World War II.
