The Greater Poland uprising of 1918-1919, or Wielkopolska uprising of 1918-1919  or Posnanian 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 was part of the Polish-Lithuanian Commonwealth before the Second Partition of Poland in 1793 when it was taken over by the German Kingdom of Prussia.

What effect did the Polish uprising have?
reconstituted Second Polish Republic