Interwar period Upon the German defeat in World War I, another
Greater Poland Uprising broke out in 1918, which aimed to incorporate the lands once annexed by Prussia into a re-established Polish state. The forces of the
Polish Military Organisation were able to oust the German administration from the bulk of the Greater Polish lands, whereafter the Posen governor (
Landeshauptmann) Ernst von Heyking was forced to retire to
Meseritz (Międzyrzecz) and
de facto only ruled over the far western, predominantly German settled districts at the border with the adjacent Prussian provinces of Pomerania, Brandenburg and Silesia. The Polish advance was halted, after the German forces had re-organised in several
Freikorps units and the demarcation line became the basis of the ruling by the 1919 Treaty of Versailles, adjudicating the parts occupied by Polish forces
uti possidetis to the
Second Polish Republic. The governmental power of the German administration was confined to the smaller western parts of Posen and West Prussia, the Prussian state government was represented by the former
Bromberg supervisor (
Regierungspräsident) Friedrich von Bülow, who relocated his administrative seat to Schneidemühl. With the entry into force of the German
Ostmark law on 1 July 1922, the province was created out of those smaller western parts of former Posen and West Prussia that remained with the Weimar Republic. In view of previous clashes of arms and the loss of territories considered German, the remaining German population in province maintained a strong
nationalistic attitude from the outset. In the provincial elections, the
German National People's Party (DNVP) emerged as the dominant political force. Friedrich von Bülow, a member of the national liberal
German People's Party, served as
Oberpräsident from the province's formal establishment in 1922 until his retirement in 1933. He was succeeded by DNVP politician Hans von Meibom from
Meseritz, who held the office until 1934, when the DNVP was dissolved as part of the
Nazi regime's
Gleichschaltung measures. Following von Meibom's removal, administrative authority over Posen–West Prussia was assumed by
Wilhelm Kube, the Nazi
Oberpräsident of neighbouring
Brandenburg. Kube, who had a reputation for corruption, administered both provinces until 1936, when he was dismissed after a political dispute with Nazi jurist
Walter Buch, the father-in-law of
Martin Bormann. Thereafter, Posen–West Prussia remained under joint administration with Brandenburg under Nazi
Oberpräsident Emil Stürtz until the province was formally dissolved on 1 October 1938. Its territory was subsequently divided between the provinces of
Silesia,
Pomerania and
Brandenburg.
World War II After the
Invasion of Poland in September 1939, the province was incorporated into the newly formed
Reichsgau Wartheland, with smaller portions absorbed into
Reichsgau Danzig-West Prussia. German civil administration replaced the short-lived military occupation, and Nazi authorities implemented a programme of forced Germanisation, expulsions of the Polish and Jewish populations, and the establishment of ghettos and camps. The former provincial structures of Posen–West Prussia were not reinstated; rather, the annexation was treated as a permanent extension of Nazi Germany, in breach of international law. Following Germany's defeat in
World War II, the entire territory that once constituted the province was placed under Polish administration in accordance with the decisions made at the
Potsdam Conference. The
Oder–Neisse line was established as the new German-Polish border, moving it considerably westward. As a result, the
former German population was subject to mass expulsion and replaced by Poles, many of whom had
themselves been displaced from areas annexed by the
Soviet Union. The former lands of Posen–West Prussia were fully integrated into the post-war Polish state, and the province ceased to exist both
de facto and
de jure. == Subdivision ==