From its inception, the Second Polish Republic struggled to secure and maintain its existence in difficult circumstances. The extraordinary complications of defining frontiers preoccupied the state in its infancy. To the southwest, Warsaw encountered boundary disputes with Czechoslovakia. More ominously, an embittered Germany begrudged any territorial loss to its new eastern neighbor. The 1919 Treaty of Versailles (see Glossary) settled the German-Polish borders in the Baltic region. The port city of Danzig, a city predominantly German but as economically vital to Poland as it had been in the sixteenth century, was declared a free city. Allied arbitration divided the ethnically mixed and highly coveted industrial and mining district of Silesia between Germany and Poland, with Poland receiving the more industrialized eastern section. These terms would be a primary incentive to the German aggression that ignited World War II.

Military force proved the determinant of Poland's frontiers in the east, a theater rendered chaotic by the repercussions of the Russian revolutions and civil war. Pilsudski envisioned a new federation with Lithuania and Polish domination of western Ukraine, centered at Kiev, forming a Polish-led East European confederation to block Russian imperialism. Vladimir I. Lenin, leader of the new communist government of Russia, saw Poland as the bridge over which communism would pass into the labor class of a disorganized postwar Germany. When Pilsudski carried out a military thrust into Ukraine in 1920, he was met by a Red Army counterattack that drove into Polish territory almost to Warsaw. Although many observers marked Poland for extinction and Bolshevization, Pilsudski halted the Soviet advance before Warsaw and resumed the offensive. The Poles were not able to exploit their new advantage fully, however they signed a compromise peace treaty at Riga in early 1921 that split disputed territory in Belorussia and Ukraine between Poland and Soviet Russia. The treaty avoided ceding historically Polish territory back to the Russians.

Data as of October 1992