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. German forces invaded Poland from the north, south, and west the morning after the Gleiwitz incident, as the Wehrmacht advanced, Polish forces withdrew from their forward bases of operation close to the Polish–German border to more established lines of defence to the east. After the mid-September Polish defeat in the Battle of the Bzura, 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. While those two countries had pacts with Poland and had declared war on Germany on 3 September, in the end their aid to Poland was very limited. The Soviet Red Armys invasion of Eastern Poland on 17 September, in accordance with a protocol of the Molotov–Ribbentrop Pact. Facing a second front, the Polish government concluded the defence of the Romanian Bridgehead was no longer feasible, on 6 October, following the Polish defeat at the Battle of Kock, German and Soviet forces gained full control over Poland. The success of the invasion marked the end of the Second Polish Republic, the Soviet Union incorporated its newly acquired areas into its constituent Belarusian and Ukrainian republics, and immediately started a campaign of sovietization. In the aftermath of the invasion, a collective of underground resistance formed the Polish Underground State within the territory of the former Polish state. Many of the exiles that managed to escape Poland subsequently joined the Polish Armed Forces in the West. On 30 January 1933, the Nazi Party, under its leader Adolf Hitler, as part of this long-term policy, Hitler at first pursued a policy of rapprochement with Poland, trying to improve opinion in Germany, culminating in the German–Polish Non-Aggression Pact of 1934. Earlier, Hitlers foreign policy worked to weaken ties between Poland and France, and attempted to manoeuvre Poland into the Anti-Comintern Pact, forming a front against the Soviet Union. The Poles feared that their independence would eventually be threatened altogether, the so-called Polish Corridor constituted land long disputed by Poland and Germany, and inhabited by a Polish majority. The Corridor had become a part of Poland after the Treaty of Versailles, many Germans also wanted the city of Danzig and its environs to be reincorporated into Germany. Danzig was a city with a German majority. It had been separated from Germany after Versailles and made into the nominally independent Free City of Danzig, the series of border violations, which are unbearable to a great power, prove that the Poles no longer are willing to respect the German frontier. Poland participated with Germany in the partition of Czechoslovakia that followed the Munich Agreement and it coerced Czechoslovakia to surrender the region of Český Těšín by issuing an ultimatum to that effect on 30 September 1938, which was accepted by Czechoslovakia on 1 October. This region had a Polish majority and had been disputed between Czechoslovakia and Poland in the aftermath of World War I, the Polish annexation of Slovak territory later served as the justification for the Slovak state to join the German invasion. Poland rejected this proposal, fearing that after accepting these demands, it would become subject to the will of Germany
Polish Infantryman, 1939
Hitler watching German soldiers marching into Poland in September 1939.