National Unity Day in Belarus Date in the current year: September 17, 2024

Western Belarus became part of Poland after the defeat of the Russian Soviet Federative Socialist Republic in the Polish–Soviet War of 1918–1921. According to the terms of the Peace of Riga, Poland was restored within the historic boundaries of the Polish–Lithuanian Commonwealth in 1772, gaining control over Western Ukraine, Western Belarus, and certain Russian territories.

In August 1939, the Soviet Union and Nazi Germany signed a non-aggression pact, commonly referred to as the Molotov–Ribbentrop Pact. It included the Secret Protocol defining the borders of German and Soviet spheres of influence in Eastern Europe. The protocol recognized the interest of the Soviet Union in Latvia, Estonia, Finland, Bessarabia, and Eastern Poland.

On September 1, 1939, Nazi Germany invaded Poland. The German invasion of Poland marked the beginning of the Second World War. Sixteen days later, a representative of the People’s Commissariat of Foreign Affairs of the Soviet Union delivered a declaration of war to the Polish ambassador in Moscow, where the Soviet invasion of Poland was explained by the need to protect the population of Western Ukraine and Western Belarus from German aggression.

The Red Army troops began to move into Poland on the morning of September 17 and met little organized resistance. Following Soviet–German negotiations, a demarcation line was established between the Soviet and German armies in Poland on September 21. On September 28, the Soviet Union and Nazi Germany signed the German–Soviet Boundary and Friendship Treaty that formalized the partition of Poland.

As a result of its invasion of Poland, the Soviet Union established control over Polish territories east of the Curzon Line (a demarcation line between Poland and the Soviet Union first proposed by the British Foreign Secretary George Curzon in 1919). The newly annexed territories had an area of 196,000 square kilometers and a population of 13.5 million people.

The territories that the Soviet government referred to as Western Ukraine and Western Belarus were “reunited” with the Ukrainian SSR and the Byelorussian SSR, respectively. Western Belarus was formally admitted to the Byelorussian Soviet Socialist Republic on November 14, 1939.

Alexander Lukashenko established National Unity Day on June 7, 2021 to commemorate the Soviet invasion of Poland and the subsequent unification of Western Belarus with the BSSR. According to his press service, the main goal of the holiday is to emphasize the continuity of generations, as well as the inviolability and self-sufficiency of the Belarusian statehood and nation.

Some historians criticized the new holiday, stressing that the annexation of Western Belarus led to Stalinist repressions in this part of the country, and the name “National Unity Day” was a clear attempt to please Russia that has a public holiday with the same name. The introduction of the holiday was also criticized by the Ministries of Foreign Affairs of Poland and Lithuania.