The Treaty of Trianon was the peace agreement signed in 1920, at the end of World War I, between the Allies of World War I and Hungary (one of the successor states to Austria-Hungary). The treaty regulated the status of an independent Hungarian state and defined its borders. Compared to the pre-war Kingdom of Hungary (which was part of Austria-Hungary), post-Trianon Hungary had 72% less territory, i.e. its area was 93,073 square kilometres (35,936 sq mi), while the area of the pre-war Kingdom of Hungary was 325,411 square kilometres (125,642 sq mi). Its population was 7.6 million, which was 64% less than the population of the pre-war kingdom, whose population was 20.9 million. 31% (3.3 out of 10.7 million) of ethnic Hungarians who lived in the pre-war kingdom lived outside the newly defined borders of post-Trianon Hungary. Compared to the pre-war kingdom, post-Trianon Hungary did not include five of ten most populous cities of the pre-war kingdom and did not have direct access to the sea. The military establishment of the post-Trianon Hungary included an army of about 35,000, while the navy of pre-war Austria-Hungary ceased to exist.
The principal beneficiaries of territorial division of pre-war Kingdom of Hungary were Romania, Czechoslovakia, and the Kingdom of Serbs, Croats and Slovenes, due to the fact that territories that were assigned to these countries were mainly populated by ethnic Romanians, Slovaks and South Slavs. In addition, the newly established state of Hungary had to pay war reparations to its neighbours. The Hungarian delegation signed the treaty under protest on 4 June 1920 at the Grand Trianon Palace in Versailles, France. In 1938 - 1940, during World-War II, post-Trianon Hungary temporarily expanded its territory and included some additional territories that formerly were part of pre-war Kingdom of Hungary, under Third Reich auspices. It was later reduced to boundaries approximating those of 1920 by the peace treaties signed after World War II at Paris, in 1947.
The treaty was registered in League of Nations Treaty Series on August 24, 1921.
Treaty of Trianon internationally guaranteed Hungarian borders.
Representatives of small nations living in the former Austria-Hungary and active in the Congress of Oppressed Nations regarded the treaty of Trianon for being an act of historical righteousness because the better future for their nations was “to be founded and durably assured on the firm basis of world democracy, real and sovereign government by the people, and an universal alliance of the nations vested with the authority of arbitration” while at the same time making a calls for putting an end to “the existing unbearable domination of one nation over the other” and making it possible “for nations to organize their relations to each other on the basis of equal rights and free conventions”. Furthermore, they believed the treaty would help toward new era of dependence on international law, the fraternity of nations, equal rights, and human liberty as well as aid civilization in the effort to free humanity from international violence.