The Polish-Soviet War (1919-1921) was a conflict between the newly established Second Polish Republic and the Soviet Russia. The war arose from territorial disputes following World War I, as both nations sought to expand their borders. The conflict was marked by significant battles, including the Battle of Warsaw in 1920, where Polish forces achieved a decisive victory, halting the Soviet advance into Europe. The war concluded with the Treaty of Riga in 1921, which divided disputed territories between Poland and Soviet Russia. This treaty solidified Poland's eastern borders and established a period of relative peace, although tensions between the two nations persisted in the following years.