The seeds of the Hungarian–Romanian war of 1919 were planted when Transylvania proclaimed union with Romania on December 1, 1918. In April 1919, the Bolsheviks came to power in Hungary, at which point its army attempted to retake Transylvania, commencing the war. By its final stage, more than 120,000 troops on both sides were involved. The destruction of the Hungarian Soviet Republic and the Romanian occupation of parts of Hungary proper, including its capital Budapest in August 1919, ended the war. Romanian troops withdrew from Hungary in March 1920.