Trianon, Treaty of, June 4, 1920, the peace treaty signed in the Grand Trianon villa at Versailles, near Paris, by Hungary and the victorious Allied powers after World War I. (The earlier Treaty of St. Germain had separated Hungary from Austria.) The terms of the treaty, greatly resented by the Hungarian people, divested Hungary of almost three-fourths of its former territory. Czechoslovakia received Slovakia and the Ruthenian region. Austria was given a strip of western Hungary called the Burgenland. The Kingdom of the Serbs, Croats, and Slovenes (later Yugoslavia) received Croatia, Slavonia, and part of the Banat. The rest of the Banat and Transylvania went to Romania.

Among other Hungarian territorial losses was the Adriatic port of Fiume (now Rijeka, Yugoslavia), Hungary's only seaport. The treaty also limited the Hungarian army to 35,000 men and provided that Hungary make reparations payments to Allied nations to compensate for war damages.