The Intermarium is a historically rooted Polish geopolitical concept centered on the creation of a strong alliance of Central and Eastern European countries along a North–South axis. The aim is to provide a strategic counterbalance to the dominant influence of Germany and Russia and to resist their imperial ambitions.

Rooted in the legacy of the Jagiellonian dynasty and the Polish-Lithuanian Commonwealth, the Intermarium concept envisions a federation of nations stretching between the Baltic, Black, and Adriatic seas. Various interpretations of the concept include the Baltic States—with Lithuania playing a particularly significant historical role—Belarus, Ukraine, the Balkan nations, and sometimes even extending as far as Greece. Poland, as the region’s largest and most influential country, is envisioned as the leading force within this alliance.

Marshal Józef Piłsudski was a staunch proponent of reviving the Intermarium idea, expanding its scope to include countries of the Caucasus. However, the outbreak of World War I and the geopolitical rearrangements following the Yalta Conference stalled these ambitions for decades, placing much of the region under Soviet domination.

Today, the Intermarium concept is experiencing a revival. Partly embodied in the modern Three Seas Initiative, it represents a renewed effort to harness regional synergies and to build a cohesive political and economic framework focused on shared objectives and long-term development security.