Short answers, pulled from the story.
The Second Polish Republic existed from the 7th of October 1918 to the 6th of October 1939, a period of exactly twenty-one years. It was established at the end of World War I and ended when organised Polish military resistance collapsed at the Battle of Kock, after invasions by Nazi Germany, the Soviet Union, and Slovakia.
Józef Piłsudski was the founding figure of the Second Polish Republic. Released from German imprisonment in Magdeburg on the 10th of November 1918, he was appointed Commander in Chief within a day and Chief of State by the 14th of November. He carried out a military coup in May 1926 and governed under the Sanacja regime until his death in 1935.
The population of the Second Polish Republic grew from 25.7 million at the 1921 census to an estimated 35.1 million by 1939. Nearly a third of the population belonged to ethnic minorities, including Ukrainians at 14%, Jews at around 10%, Belarusians at 3%, and Germans at 2%. By 1931, Poland held the second largest Jewish population in the world.
In 1924, Prime Minister Władysław Grabski introduced the złoty as a single common currency, replacing five currencies, and Poland became the only European country to control its hyperinflation without foreign loans. Recovery from the Great Depression was led by economist Eugeniusz Kwiatkowski through three major projects: the Gdynia seaport, the 500-kilometre Polish Coal Trunk-Line, and the Central Industrial Region.
Treatment of Jews deteriorated sharply after Piłsudski's death in 1935. The National Democracy movement passed resolutions in 1937 declaring the removal of Jews from social, economic, and cultural life their primary goal. The Camp of National Unity drafted anti-Semitic legislation in 1938 modelled on laws in Germany, Hungary, and Romania. Historian William W. Hagen assessed that by 1939, Polish Jews faced conditions comparable to those under Nazi rule.
Germany and Slovakia attacked Poland on the 1st of September 1939, one week after the Molotov-Ribbentrop Pact was signed. Warsaw fell on the 28th of September after a twenty-day siege. The Soviet Union invaded from the east on the 17th of September. Organised resistance ended on the 6th of October 1939 at the Battle of Kock. Poland did not surrender; a government-in-exile operated in London until 1990.