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 (a successor state to Austria-Hungary). The treaty greatly redefined and reduced Hungary's borders. From its borders before World War I, it lost 72% of its territory, which was reduced from 325,111 square kilometres (125,526 sq mi) to 93,073 square kilometres (35,936 sq mi).
It also lost 64% of its total population, which was reduced from 20.9 million to 7.6 million, and 31% (3.3 out of 10.7 million) of its ethnic Hungarians, who suddenly found themselves living outside the newly defined borders of Hungary. Hungary lost five of its ten most populous cities and was deprived of direct access to the sea and of some of its most valuable natural resources.
The principal beneficiaries of territorial adjustment were Romania, Czechoslovakia, and the Kingdom of Serbs, Croats and Slovenes. 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.
Transylvania and other Hungarian territories like Bánság, Kőrösvidék and Máramaros were attached to Romania.
“Transylvanism” is an ideological movement created in 1921 by Károly Kós, a polymath leader (architect, writer and publisher) of the Hungarian minority. He urged for political loyalty towards the new ruler of Transylvania, the Romanian state, without giving up the Hungarian cultural identity. His manifesto called “Crying Word” (a clear reference to the biblical phrase of “The Voice of One Crying”, or “Kiáltó szó” in Hungarian) became an important guide of consolation for the loss of the mother country, and an ideology to re-organize the Transylvanian Hungarian community.