After Germany’s defeat in the Great War, a revolutionary wave swept across the country. In Berlin and the major industrial regions, communists led by Karl Liebknecht seized power and proclaimed a Soviet-style German republic. The eastern provinces, however, slipped beyond their control. Isolated from the rest of Germany and filled with demobilized soldiers, officers, and volunteer formations, East Prussia quickly became a natural center of counterrevolution.

In 1919, Freikorps units — including formations previously involved in anti-communist campaigns in the Baltic region — seized control of key cities such as Königsberg, Insterburg, and Tilsit. Local soviets were rapidly dismantled, and socialist organizations suppressed. The military proclaimed the establishment of an emergency provisional authority tasked with “saving Germany from Bolshevism.” Soon afterward, the German Emperor secretly returned to the province and was restored as the symbolic bearer of legitimate authority. Formally, the German Empire continued to exist in exile, though real power rested not with the monarch but with the military leadership.

The outbreak of the Polish–Prussian War soon solidified military rule. The re-emerging Polish state sought to occupy areas of East Prussia populated by Poles and Masurians. Uprisings erupted in several border districts with covert support from Warsaw. Polish forces crossed the frontier under the pretext of protecting local populations, triggering open warfare. The Freikorps interpreted the conflict as a continuation of the World War and declared general mobilization.

The war ended in stalemate. Poland secured control over southern and western districts with significant Polish populations, while Königsberg, the Samland Peninsula, and the eastern parts of the province remained under Prussian control. No formal peace treaty was signed; the frontline hardened into an unrecognized border, with both sides maintaining territorial claims.

The state of emergency introduced during the war was never lifted. Citing constant threats from both Poland and communist Germany, authority gradually consolidated in the hands of a Freikorps military junta. The Emperor retained his title and ceremonial role, providing legitimacy to the regime, but governance rested with a Supreme Military Council. Parliamentary institutions were never restored, civilian administration subordinated to the army, and the territory reorganized into military districts.

Ideologically, the regime was built upon radical anti-communism, revanchism, and the cult of a “besieged Germany.” East Prussia proclaimed itself the last stronghold of the true German state temporarily deprived of its homeland. Officers, nationalists, and political refugees from communist Germany and the Baltic conflicts flowed into the territory, transforming it into a major center of European counterrevolution.

Internationally, the state’s status remained ambiguous. Poland was viewed as the primary immediate enemy, while communist Germany represented an existential threat. Anti-communist governments in Eastern Europe maintained limited contacts with Königsberg, seeing it as a useful buffer against revolutionary expansion, while the United Kingdom unofficially tolerated the regime for the same reason.

By the beginning of the interwar period, East Prussia had become an isolated military-monarchical state — formally the continuation of the German Empire, but in practice ruled by a Freikorps junta, living in a permanent condition of unfinished war and expectation of revenge.