The First World War (1914-1918) brought defeat to the three powers that had occupied Poland divided by 123 years. While Germany and Austria left defeated at war's end in 1918, in Russia the Bolshevik Revolution plunges the country into a bloody civil war since 1917. In November 1918, after more than a century of slavery, finally Poland regains its independence.
On 27 December 1918, breaks out in Poznan Polish revolt against the the Republic of Weimar, which replaced the German monarchy abolished soon the end of the Great War. The fighting took place between Polish soldiers (were once part of the Prussian military body) against the Germans, who were demoralized by defeat in war.
From late 1918 to June 1919 the Poles were involved in conflict with the Germans until the signing of the Versailles Treaty that served them ceasefire. While the Poles were at war with the People's Republic of Ukraine (1918-1918).
After winning the Ukrainians in July 1919, the Red Army of Russia now communist threat invade Poland with the purpose of releasing it from the "bourgeois government" considered counterrevolutionary.
For some members of the Russian Communist government in the Kremlin, Poland is an obstacle and should be eliminated so that there is way to socialist revolution should spread around Europe and then the world. In the same year arises the alliance between Poland and the People's Republic Ukrainian against Russian Bolshevik government.
- Second Polish Republic;
- Russian Soviet Federative Socialist Republic (Russian SFSR);
- People's Republic of Ukraine;
- Ukrainian Soviet Socialist Republic (Ukrainian SSR);
- Republic of Weimar (Germany) - available only against the Polish insurrection;