The war split the ranks of the three partitioning empires, pitting Russia as defender of Serbia and ally of Britain and France against the leading members of the Central Powers, Germany and Austria-Hungary. This circumstance afforded the Poles political leverage as both sides offered pledges of concessions and future autonomy in exchange for Polish loyalty and recruits. The Austrians wanted to incorporate Congress Poland into their territory of Galicia, so they allowed nationalist organizations to form there. The Russians recognized the Polish right to autonomy and allowed formation of the Polish National Committee, which supported the Russian side. In 1916, attempting to increase Polish support for the Central Powers, the German and Austrian emperors declared a new kingdom of Poland. The new kingdom included only a small part of the old commonwealth, however.

As the war settled into a long stalemate, the issue of Polish self-rule gained greater urgency. Roman Dmowski spent the war years in Western Europe, hoping to persuade the Allies to unify the Polish lands under Russian rule as an initial step toward liberation. In the meantime, Pilsudski had correctly predicted that the war would ruin all three of the partitioners, a conclusion most people thought highly unlikely before 1918. Pilsudski therefore formed Polish legions to assist the Central Powers in defeating Russia as the first step toward full independence for Poland.

Much of the heavy fighting on the war's Eastern Front took place on the territory of the former Polish state. In 1914 Russian forces advanced very close to Kraków before being beaten back. The next spring, heavy fighting occurred around Gorlice and Przemysl, to the east of Kraków in Galicia. By the end of 1915, the Germans had occupied the entire Russian sector, including Warsaw. In 1916 another Russian offensive in Galicia exacerbated the already desperate situation of civilians in the war zone; about 1 million Polish refugees fled eastward behind Russian lines during the war. Although the Russian offensive of 1916 caught the Germans and Austrians by surprise, poor communications and logistics prevented the Russians from taking full advantage of their situation.

A total of 2 million Polish troops fought with the armies of the three occupying powers, and 450,000 died. Several hundred thousand Polish civilians were moved to labor camps in Germany. The scorched-earth retreat strategies of both sides left much of the war zone uninhabitable.

Data as of October 1992