Borders of Hungary
Drafted borders of Austria-Hungary in the treaty of Trianon and Saint Germain.
The Hungarian government terminated its union with Austria on 31 October 1918, officially dissolving the Austro-Hungarian state. The de facto temporary borders of independent Hungary were defined by the ceasefire lines in November–December 1918. Compared with the pre-war Kingdom of Hungary, these temporary borders did not include:
- Part of Transylvania south of the Mureş river and east of the Someş river, which came under the control of Romania (cease-fire agreement of Belgrade signed on 13 November 1918). On 1 December 1918, the National Assembly of Romanians in Transylvania declared union with the Kingdom of Romania.
- Slovakia, which became part of Czechoslovakia (status quo set by the Czechoslovak legions and accepted by the Entente on 25 November 1918). Afterwards, the Slovak politician Milan Hodža discussed with the Hungarian Minister of Defence, Albert Bartha, a temporary demarcation line that had not followed the Slovak-Hungarian linguistic border, and left more than 900,000 Hungarians in the newly formed Czechoslovakia. That was signed on 6 December 1918.
- South Slavic lands, which, after the war, were organised into two political formations – the State of Slovenes, Croats and Serbs and Banat, Bačka and Baranja, which both came under control of South Slavs, according to the ceasefire agreement of Belgrade signed on 13 November 1918. Previously, on 29 October 1918, the Kingdom of Croatia-Slavonia parliament, an autonomous kingdom within the Transleithania, terminated the union with the Kingdom of Hungary and on 30 October 1918 the Hungarian diet adopted a motion declaring that the constitutional relations between the two states had ended.
Croatia-Slavonia was included in a newly formed State of Slovenes, Croats, and Serbs (which also included some other South Slavic territories, formerly administered by Austria-Hungary) on 29 October 1918. This state and the Kingdom of Serbia formed the Kingdom of Serbs, Croats and Slovenes (Yugoslavia) on 1 December 1918.
The territories of Banat, Bačka and Baranja (which included most of the pre-war Hungarian counties of Baranya, Bács-Bodrog, Torontál, and Temes) came under military control by the Kingdom of Serbia and political control by local South Slavs. The Great People's Assembly of Serbs, Bunjevci, and other Slavs from Banat, Bačkam and Baranja declared union of this region with Serbia on 25 November 1918. The ceasefire line had the character of a temporary international border until the treaty. The central parts of Banat were later assigned to Romania, respecting the wishes of Romanians from this area, which, on 1 December 1918, were present in the National Assembly of Romanians in Alba Iulia, which voted for union with the Kingdom of Romania.
- The city of Fiume (Rijeka) was occupied by the Italian nationalists group. Its affiliation was a matter of international dispute between the Kingdom of Italy and Yugoslavia.
- Croatian-populated territories in modern Međimurje remained under Hungarian control after the ceasefire agreement of Belgrade from 13 November 1918. After the military victory of Croatian forces led by Slavko Kvaternik in Međimurje against Hungarian forces, this region voted in the Great Assembly of 9 January 1919 for separation from Hungary and entry into Yugoslavia.
After the Romanian Army advanced beyond this cease-fire line, the Entente powers asked Hungary (Vix Note) to acknowledge the new Romanian territory gains by a new line set along the Tisza river. Unable to reject these terms and unwilling to accept them, the leaders of the Hungarian Democratic Republic resigned and the Communists seized power. In spite of the country being under Allied blockade, the Hungarian Soviet Republic was formed and the Hungarian Red Army was rapidly set up. This army was initially successful against the Czechoslovak Legions, due to covert food and arms aid from Italy. This made it possible for Hungary to reach nearly the former Galician (Polish) border, thus separating the Czechoslovak and Romanian troops from each other.
After a Hungarian-Czechoslovak cease-fire signed on 1 July 1919, the Hungarian Red Army left parts of Slovakia by 4 July, as the Entente powers promised to invite a Hungarian delegation to the Versailles Peace Conference. In the end, this particular invitation was not issued. Béla Kun, leader of the Hungarian Soviet Republic, then turned the Hungarian Red Army on the Romanian Army and attacked at the Tisza river on 20 July 1919. After fierce fighting that lasted some five days, the Hungarian Red Army collapsed. The Royal Romanian Army marched into Budapest on 4 August 1919.
The Hungarian state was restored by the Entente powers, helping Admiral Horthy into power in November 1919. On 1 December 1919, the Hungarian delegation was officially invited to the Versailles Peace Conference; however, the newly defined borders of Hungary were nearly concluded without the presence of the Hungarians. During prior negotiations, the Hungarian party, along with the Austrian, advocated the American principle of self-determination: that the population of disputed territories should decide by free plebiscite to which country they wished to belong. This view did not prevail for long, as it was disregarded by the decisive French and British delegates. According to some opinions, the Allies drafted the outline of the new frontiers  with little or no regard to the historical, cultural, ethnic, geographic, economic and strategic aspects of the region. The Allies assigned territories that were mostly populated by non-Hungarian ethnicities to successor states, but also allowed these states to absorb sizeable territories that were mainly inhabited by Hungarian-speaking populations. For instance, Romania gained all of Transylvania, which was home to 2,800,000 Romanians, but also contained a significant minority of 1,600,000 Hungarians and about 250,000 Germans. The intent of the Allies was principally to strengthen these successor states at the expense of Hungary. Although the countries that were the main beneficiaries of the treaty partially noted the issues, the Hungarian delegates tried to draw attention to them. Their views were disregarded by the Allied representatives.
Some predominantly Hungarian settlements, consisting of more than two million people, were situated in a typically 20–50 km (12–31 mi) wide strip along the new borders in foreign territory. More concentrated groups were found in Czechoslovakia (parts of southern Slovakia), Yugoslavia (parts of northern Vojvodina), and Romania (parts of Transylvania).
The final borders of Hungary were defined by the Treaty of Trianon signed on 4 June 1920. Beside exclusion of the previously mentioned territories, they did not include:
By the Treaty of Trianon, the cities of Pécs, Mohács, Baja and Szigetvár, which were under Serb-Croat-Slovene administration after November 1918, were assigned to Hungary. An arbitration committee in 1920 assigned small northern parts of the former Árva and Szepes counties of the Kingdom of Hungary with Polish majority population to Poland. After 1918, Hungary did not have access to the sea, which pre-war Hungary formerly had directly through the Rijeka coastline and indirectly through Croatia-Slavonia.
With the help of Nazi Germany and Fascist Italy, Hungary expanded its borders towards neighbouring countries at the outset of World War II. This started under the Munich Agreement (1938), then the two Vienna Awards (1938 and 1940), and was continued with the dissolution of Czechoslovakia (occupation of northern Carpathian Ruthenia and eastern Slovakia) and the Axis invasion of Yugoslavia. This territorial expansion was short-lived, since the post-war Hungarian boundaries in the Paris Peace Treaties, 1947 were nearly identical to those of 1920 (with three villages – Jarovce, Rusovce, and Čunovo – transferred to Czechoslovakia).
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 a 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 a universal alliance of the nations vested with the authority of arbitration" while at the same time making a call 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 a new era of dependence on international law, the fraternity of nations, equal rights, and human liberty as well as aid civilisation in the effort to free humanity from international violence.