Piłsudski formed a new centralised government and went on to command Polish forces against Russia in the victorious 1920 Battle of Warsaw, a key turning point in the rebirth of the country. In true facepalm fashion, however, Independence Day was constituted in 1937 and celebrated exactly twice before World War II began and Poland found itself occupied again. In the communist era, the date of Independence Day was dubiously moved to July 22nd to honour the day the PKWN Manifesto - a document which basically asserted communist authority over Poland - was issued in 1944. After communism fell in 1989, the holiday was restored to its original November 11th date.
If you're in Poland on this day you'll find that though a national bank holiday, most restaurants and bars will still be open. Marking the occasion in Kraków each year is a holy mass at Wawel Cathedral (10:00), followed by a very solemn military parade at 11:30 from Wawel to Plac Matejki, along the Royal Route. In the evening things are a bit more lively as the Loch Camelot cabaret hands out free songbooks and leads the people in the singing of patriotic songs on the market square, beginning at 15:00.