The Treaty of Warsaw of April 1920 was a military-economical alliance between the Second Polish Republic, represented by Józef Piłsudski, and the Ukrainian People's Republic, represented by Symon Petliura, against Bolshevik Russia. The treaty was signed on 21 April 1920, with a military addendum on 24 April.

Józef Klemens Piłsudski[a] was a Polish statesman who served as the Chief of State (1918–1922) and first Marshal of Poland. In the aftermath of World War I, he became an increasingly dominant figure in Polish politics and exerted significant influence on shaping the country's foreign policy. Piłsudski is viewed as a father of the Second Polish Republic, which was re-established in 1918, 123 years after the final partition of Poland in 1795, and was considered de facto leader (1926–1935) of the Second Republic as the Minister of Military Affairs.