Romanian cavalry in Budapest.
August 3 1919, Budapest–After committing their reserves, the Romanians were easily able to drive the Hungarians back to the Tisza. On August 1, after receiving clearance to do so from the Allies, the Romanians crossed the river, and found little resistance from the Hungarians. Béla Kun fled for Austria, where he was interned for a time before being sent to Russia. A more moderate Social Democrat government took over, but it was too late; Romanian cavalry units entered the capital on August 3, and the Romanians would remain until November. With tacit Romanian approval, the Social Democrats were deposed by more conservative elements, who supported a Habsburg restoration under Archduke Joseph August. The Allies refused to allow a Habsburg on the throne (or as regent) of Hungary, however.
The Romanians did not occupy the entirety of the country; they were content to leave portions out the southwest to Admiral Horthy’s National Army. Horthy remained a rival to the conservative government in the capital, and began a “White Terror” against Communists, Social Democrats, and Jews perceived to have supported Béla Kun.
Sources include: Glenn E. Torrey, The Romanian Battlefront in World War I.