1848
After the defeat of Congress Poland, many Prussian liberals sympathised with the demand for the restoration of the Polish state. In the spring of 1848 the new liberal Prussian government allowed some autonomy to the Grand Duchy of Posen in the hope of contributing to the cause of a new Polish homeland. Due to a number of factors, including the outrage of the German-speaking minority in Pozen, the Prussian government reversed course. By April 1848, the Prussian army had already suppressed the Polish militias and National Committees that emerged in March. By the end of the year the Duchy had lost the last vestiges of its formal autonomy, and was downgraded to a Province of the Prussian kingdom.
Read more about this topic: Territorial Evolution Of Poland