Second Republic in 1921 borders had 388.6 thousands square km of area (6th place in Europe) and 27.2 milion inhabitants. In 1939, just before war, it had 35.1 milion inhabitants. About 1/3 of this were national minorities.
Just before World War I ended, Rada Regencyjna in 7 October 1918 published manifesto to Polish nation, in which it announced its support for independence of Poland. With notable exception of SDKPiL, most parties supported this move.
In 6 November communists announced creation of Republic of Tarnobrzeg. The same day Temporary People's Government of Republic of Poland under Ignacy Daszynski was created.
In 10 November Pilsudski, freed from Magdenburg prison returned to Warsaw. Because of is popularity and support from most political parties, Rada Regencyjna gave Pildudski Highest Command over Polish Army the next day. In 14 November Rada Regencyjna dissolved and transfered all its authority to Pilsudski.
After consultation with Pilsudski, Daszynski's government dissolved and new government was created under Andrzej Moraczewski.
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Elections of Sejm - 26 January 1919
War against Soviets.
Uprisings in Wielkopolska and Silesia.
15 July 1920 - Agrarian Reform.
17 March 1921 - March Constitution
Election to Sejm and Setnat - November 1922.
President Narutowicz, and assasitanion of him (16 December 1922)
President Wojciechowski - 20 December 1922 to Zamach majowy
and so on..., it needs turning into real article, more details and extending to next years