On this day, 104 years ago, March 18, 1921 (February 9, 1921 in the lunar calendar), the Polish-Soviet War ended. The Polish-Soviet War (February 1919-March 18, 1921) was a war fought after the end of World War I between two newly established regimes, the Russian Soviet Federal Socialist Republic and the Second Polish Republic. The war was caused by the two countries 'attempts to expand their territory and influence. The Treaty of Versailles re-established Poland since its partition in the late 18th century, and Poland, which had just regained its independence, sought to preserve the territory it lost during the partition; The goal of the Russian Soviet Federal Socialist Republic (hereinafter: Soviet Russia) was to control the same territories that were once part of the Russian Empire until World War I. Both countries claimed victory [1]. In this war, the Poles claimed to have successfully defended their country, while the Soviet Union claimed that Poland's eastward incursion into Ukraine and Belarus was repelled, believing it to be part of the Allied armed intervention in the Russian Civil War. The border between Poland and Soviet Russia was not detailed in the Treaty of Versailles. Post-war riots: the Russian Revolution of 1917; The collapse of the Russian Empire, the German Empire, and the Austro-Hungarian Empire; the Russian Civil War; the withdrawal of the Allies from the Eastern Front; attempts at independence for Ukraine and Belarus. Poland's head of state, Joseph Piłsudski, believed that this was a good opportunity for Poland to expand its territory eastward and planned to establish a Polishized alliance by uniting the rest of Central and Eastern European countries. dzymorze, which literally means "between the seas" and according to Pythagore's plan means from the Baltic Sea to the Black Sea), serves as a breakwater against the potential threat of the resurgence of German and Russian imperialism. Vladimir Lenin believed that the Red Army could support the German Communist Party through Poland and create revolutions elsewhere in Europe. In 1919, Polish troops controlled most of Western Ukraine and won the Polish-Ukrainian War. Attempts to establish a Ukraine state, the People's Republic of Western Ukraine, on a map demanded by both Poles and Ukraine failed. At the same time, the Bolsheviks gained advantage in the civil war and attacked disputed territory westward. At the end of 1919, a clear front line was formed. Small border conflicts gradually escalated. In April 1920, Piłsudsky invaded Ukraine eastward and began an open war. Almost at the same time, the Soviet army had begun a counterattack. The initial counterattack was very successful and the Soviet army entered near Warsaw, the capital of Poland. At this time, Western countries were worried that Soviet troops would reach the German border and became more interested in the Polish-Soviet War. In mid-summer, Warsaw seemed to fall, but in mid-August the situation reversed again and the Polish army achieved an unexpected and decisive victory in the Battle of Warsaw. The Polish army advancing eastward won one after another, and the Soviet Union proposed peace. In October 1920, the two sides ceasefire. The formal peace treaty, the Treaty of Riga, was signed on March 18, 1921, delimiting the disputed border between Poland and the Soviet Union. This war largely determined the Polish-Soviet border between the two world wars.