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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 (also called the Grand Duchy of Poznań or Provinz Posen region) against Germany and Prussia.

Background
The defeat of the Germany Army on the Western Front in the autumn of 1918 ignited Polish hopes for a sovereign Poland and Poles began serious preparations for an uprising after the Kaiser Wilhelm's abdication on 9 November 1918, which saw the end of the German monarchy, which would be replaced by the Weimar Republic.
The uprising broke out on on 27 December 1918 in Poznań after a patriotic speech by Ignacy Paderewski, a famous Polish pianist.
The uprising forces consisted of members of the Polish Military Organization of the Prussian Partition, who started to form the Straż Obywatelska (Citizen's Guard), later renamed as Straż Ludowa (People's Guard) and many volunteers — mainly veterans of World War I. The ruling body was the Naczelna Rada Ludowa (High Peoples' Council) — at the beginning members of the Council were against the uprising, but supported it a few days later: unofficially 3 January 1919; officially 8 and 9 January 1919 — and the military commanders: Captain Stanisław Taczak (promoted to major, temporary commander 28 December 1918 – 8 January 1919) and later General Józef Dowbor-Muśnicki.
The timing of the uprising was fortuitous, as between October 1918 and the first months of 1919, internal conflict had weakened Germany, with soldiers and sailors rebelling against the monarchy and its hawkish generals. Demoralised by the signing of an armistice on November 11, 1918, Germany was embroiled in the German Revolution.
By 15 January 1919, the rebellious Polish forces managed to take control of most of the Province of Posen, and engaged in heavy fighting with the regular German army and the forces of the Grenzschutz, up until the renewal of the truce between the Entente and Germany on 16 February, which affected the Wielkopolska or Posen Province part of the front line. Skirmishes continued, however, until the signing of the Treaty of Versailles on June 28, 1919.
Many of the Wielkopolska insurgents also took part in the 1919 - 1921 uprisings in Silesia.

The uprising
The Greater Poland Uprising is considered to be one of the two most successful Polish uprisings: the second was the Great Poland Uprising of 1806 which was ended by the entry of Napoleon's Army.
Although it never recovered the entire Prussian Partition, the uprising had a significant effect on the Versailles decisions, which granted Poland not only the area won by the insurgents but also a portion of the Province of Pomerania and the towns of Bydgoszcz, Leszno, and Rawicz (the Polish Corridor).
Germany's territorial losses as required by the Treaty of Versailles nonetheless incited German revanchism such that the status of the independent city-state Danzig (Gdańsk) and the Polish Corridor between East Prussia and the rest of Germany became a major issue in German politics, and was exploited by Adolf Hitler in his rise to power. Hitler ultimately invaded Poland in September 1939, sparking World War II.

Appraisal

Timeline of uprising

January 1916 – creation of Secret Inter-Party Citizen's Committee (pl. Tajny Międzypartyjny Komitet Obywatelski) formed by members of the German Reichstag of Polish nationality.
July 1918 – network of local Citizens' Committees is created on area of Prussian Partition.
11 October 1918 – Polish organizations in the German Empire publicize common documents in which they declare the will to create independent Polish state; in effect, revolution.
9 November 1918 – beginning of the German Revolution, which also occurred in Greater Poland. Poles organized secret military structures in the Poznań garrison, Jarocin and Inowrocław.
10 November 1918 – events of the so-called Republika Ostrowska.
11 November 1918

• Armistice signed, ending hostilities of World War I.
  The Citizens' Guard (Straż Obywatelska), renamed a few days later to The People's Guard (Straż Ludowa) comes out from the underground. The Mayor of Poznań (Posen) Ernst Wilms is removed from office. German military authorities give permission for functioning of the People's Guard to keep peace in the Province of Posen.
  12 November 1918
  
  
  
  • The Central Citizen's Committee, later renamed to the High People's Council (Naczelna Rada Ludowa, NRL), creates temporary "government-in-waiting" – Commission (Komisariat): Stanisław Adamski, Wojciech Korfanty and Adam Poszwiński.
    Jarogniew Drwęski becomes the Mayor of Poznań.
    13 November 1918
    
    
    
    • Commission of the High People's Council calls citizens of German portion of Poland to keep calm in spite of the revolution.
      "Assassination on City Hall" – as it was dominated by Germans, the Execution Department of Worker's and Soldier's Council proceeded to Poznań's City Hall, an armed group of Poles forced them to change four of the German Delegates with Poles: Bohdan Hulewicz, Mieczysław Paluch, Henryk Śniegocki and Zygmunt Wiza. Due to this event, Poles gain control over the headquarters of Poznań Garrison and 5th Corps.
      17 November 1918 – Commission of NRL calls for a one-time collection of money called a "national tax".
      18 November 1918 – elections to Poviat's People's Councils and members of the Partition's Sejm (1399 MPs).
      20 November 1918 – in exposé of the Polish government in Warsaw: przyłączenie Wielkopolski będzie jednym z pierwszych naszych zadań (the joining of Greater Poland will be one of our first tasks).
      3 December 1918 – The Partition Sejm of Poznań began official proceedings, in building of the "Apollo" Cinema. MPs were representing all lands of the Prussian Partition and Polish economic emigration, mainly from Westfalen.
      5 December 1918 – end of the Partition Sejm, which declared it's wanting of unification with the other partitions in a renationalized Poland and with NRL officially electing its members.
      6 December 1918 – first meeting of the NRL elected. Bolesław Krysiewicz becomes a Speaker. Election of executive body – Commission of NRL formed by representatives of: Greater Poland - Stanisław Adamski and Władysław Seyda; Upper Silesia – Wojciech Korfanty and Józef Rymer; Eastern Pomerania – Stefan Łaszewski; Kuyavia – Adam Poszwiński.
      11 December 1918 – Polish language and teaching of religion in Polish returns to schools.
      15 December 1918 – Polish government in Warsaw breaks diplomatic relations with Germany. Between ceasefire and reunification
      
      24 March 2005 – last Polish fighter of uprising, Lieutenant Jan Rzepa, dies at age 106.