Intermarium was a post-World War I geopolitical plan conceived by Józef Piłsudski to unite former Polish–Lithuanian Commonwealth lands within a single polity. The plan went through several iterations, some of which anticipated the inclusion of neighbouring states. The proposed multinational polity would have incorporated territories lying between the Baltic, Black, and Adriatic Seas, hence the name Intermarium.

Józef Klemens Piłsudski[a] was a Polish statesman who served as the Chief of State (1918–1922) and first Marshal of Poland. In the aftermath of World War I, he became an increasingly dominant figure in Polish politics and exerted significant influence on shaping the country's foreign policy. Piłsudski is viewed as a father of the Second Polish Republic, which was re-established in 1918, 123 years after the final partition of Poland in 1795, and was considered de facto leader (1926–1935) of the Second Republic as the Minister of Military Affairs.