In 1920 after 4 years of building resentment and anger against the brutal occupying government of the German Empire. In a desperate bid to gain Polish independence, head of the polish nationalist movement and a pro- Russian, Jozef Pilsudski made contact with Russian Republic in 1919 and the French Republic later on and they both agreed to fund him to work at leading an uprising in Poland.
He returned to Poland and while in hiding started building up support among groups and called for a unified front. His large stack of weapons and funds helped him progress to be head of the resistance. On the 18 August 1920 after a year of preparation at Z hour which was 4:00 am local time. A force comprising of Poles from all walks of life and areas had been assembling outside Warsaw since dusk. The rebel force entered from the South East of the city. While in the city the urban dwellers moved out on the streets and started erecting mock barricades and defenses to slow down the German response.
The Germans had known for a while that a rebellion was brewing but they were unaware of the timing or the amount of arms and men involved. Although the Poles take half the city, the Germans begin to organize themselves better and it devolves into violent street fighting with the Poles make a lot slower progress. In other large cities although rebellions are held due to most of the Franco- Russian arms being used for Warsaw only Lublin is taken for the rebels although all of the countryside is taken by peasants.
Up until this point the Kaiser plan had been to just hold onto the big cities and then send in troops from the rest of the Empire to crush the rebellion. As the Rebellion raged throughout later August and mid September the might of Germany finally moved into crush the Polish rebellion.
On the 19th September a German force crosses the border and starts the burning to Warsaw. Germans troops march through Poland raping, killing and burning everything they see in their paths. Mass refugees start to flee to Russia as people in their hundreds of thousands flee. The relief force reaches Warsaw to discover upon hearing what was heading for them Pilsudski having already abandoned Warsaw and fled to Russia.
Though the rebellion was crushed with few German casualties the socialists back in Germany roar in outrage about the violence used and Poland with a lot less citizens and much of the land ruined is worth a lot less as an area.