Hitler's attack on Poland was postponed once, halted almost in mid-leap
German troops were due to cross into Poland at 4:00 a.m. on 26 August 1939. Then Britain signed a fresh pact pledging to defend Polish independence, and Hitler hesitated, pushing the attack back to 1 September. One sabotage team never got the recall and struck a Silesian railway station anyway, only to be driven off.
The pieces had been moving for years. Hitler signed a non-aggression pact with Poland in 1934 while seeking to pull it into an anti-Soviet bloc as a dependent client. By 1937 Berlin was pressing for Danzig, a German-majority free city since Versailles, and for a road across the Polish Corridor to East Prussia. Warsaw refused, fearing it would share Czechoslovakia's fate, and on 31 March 1939 allied with Britain and France. Hitler scrapped the 1934 pact on 28 April and told his generals in private that Danzig was a pretext; his real goal was living space in the east.
The decisive surprise came on 24 August, when Germany and the Soviet Union signed the Molotov–Ribbentrop Pact. A secret protocol split Poland, roughly the western third to Germany and the eastern two-thirds to Moscow. After the staged Gleiwitz incident, German and Slovak forces attacked from three sides on 1 September. Britain and France declared war two days later, but their help amounted to little beyond a limited French push into the Saar.
Polish troops fell back to eastern defensive lines, and after defeat at the Bzura in mid-September they planned a long stand in the southeast, near the Romanian border. On 17 September the Red Army crossed the eastern frontier, wrecking that plan, and the government ordered its forces into neutral Romania. The last battle, at Kock, ended on 6 October. Poland never formally surrendered.
Two days later Germany annexed western Poland and Danzig and placed the rest under a new General Government, while the Soviets absorbed their share into the Byelorussian and Ukrainian republics. The Nazi aim was to erase Poland as a state and destroy its people. Resistance persisted through the clandestine Polish Underground State and through exiles who fought on in the Polish Armed Forces in the West.
Source: Invasion of Poland