Piłsudski's post-World War I Intermarium concept ranging from the Baltic sea in the north to the Mediterranean and Black Seas in the south. In light green: eastern parts of Ukrainian and Belarusian lands incorporated into the Soviet Union in 1922. Intermarium (Polish: Międzymorze, Polish pronunciation: [mʲɛnd͡zɨˈmɔʐɛ]) was a post-World War I geopolitical plan conceived by Józef Piłsudski to unite