Greater Poland Uprising (1918-1919)

The Greater Poland uprising of 1918–1919, or Wielkopolska uprising of 1918–1919 (Polish: powstanie wielkopolskie 1918–19 roku; German: Großpolnischer Aufstand) or Posnanian War was a military insurrection of Poles in the Greater Poland region (German: Grand Duchy of Poznań or Provinz Posen) 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.

After the Third Partition of Poland in 1795, the Polish nation had ceased to exist as an independent state. From 1795 through the beginning of World War I, several unsuccessful uprisings to regain independence took place. A 1806 uprising was followed by the creation of the Duchy of Warsaw which lasted for eight years before being partitioned again between Prussia and Russia. Under the oppressive German rule Poles faced systematic discrimination and oppression. The Poles living in the region of Greater Poland were subjected to Germanisation and land confiscations to make way for German colonization.

At the end of World War I, United States President Woodrow Wilson's Fourteen Points and the idea of national self-determination were met with opposition from European powers standing to lose influence or territory—this included Germany and its domination of Greater Poland. German politicians had signed an armistice leading to a ceasefire on 11 November 1918. Also, Germany had signed the Treaty of Brest-Litovsk with the Bolshevik Russia to settle the territorial boundaries of the eastern frontiers. The Brest-Litovsk treaty did not take into consideration a future Polish state, therefore from the date that the armistice was signed until the Treaty of Versailles was fully ratified in January 1920, many of the territorial and sovereignty issues remained unresolved.

...
Wikipedia