Treaty of Trianon

The Treaty of Trianon was an agreement following World War I, which was supposed to regulate the post-war situation of the Hungarian state. It was signed on June 4, 1920, at the Grand Trianon Palace at Versailles, France, reducing the size and population of Hungary by about two thirds. Hungary lost nearly all territories, which were not inhabited solely by Magyar population, leaving thus sizeable minorities in the adjecent countries:

Transylvania, the adjoing plains (the Partium), and parts of the Banat (including Timisoara) went to Romania
Czechoslovakia received Slovakia and Ruthenia
the new born state of Yugoslavia received Croatia, Slavonia, and the western section of the Banat
Austria was awarded the Burgenland; the city of Sopron and surrounding areas were returned to Hungary after a plebiscite held in 1921

The treaty was also meant to paralyse Hungarian economy and infrastructure (borders, especially towards Romania, were drawn so, that important railway lines and main roads were just out of Hungary's territory), considering Hungary an agressor in World War I.

Due to the treaty, Hungary lost its access to the sea and became a landlocked state. Further provisions stated that its army be limited to 35,000 men, or that no railway shall be built with more than one track.

Hungary recovered some of the lost territories at the wake of World War II in 1939-1940, mainly upon the Agreements of Vienna, but the new boundaries agreed on at the Treaty of Paris in 1947 were nearly indentical with those of 1920.