The Great Poland Uprising against the Germans begins.

The Greater Poland uprising of 1918–1919, or Wielkopolska uprising of 1918–1919 or Poznań War was a military insurrection of Poles in the Greater Poland region against German rule. The uprising had a significant effect on the Treaty of Versailles, which granted a reconstituted Second Polish Republic the area won by the Polish insurrectionists. The region had been part of the Kingdom of Poland and then Polish–Lithuanian Commonwealth before the 1793 Second Partition of Poland when it was annexed by the German Kingdom of Prussia. It had also, following the 1806 Greater Poland uprising, been part of the Duchy of Warsaw (1807–1815), a French client state during the Napoleonic Wars.