Union of Transylvania with Romania

The Union of Transylvania with Romania was declared on 1 December 1918 (N.S., 18 November O.S.) by the assembly of the delegates of ethnic Romanians held in Alba Iulia. The Great Union Day (also called "Unification Day"), celebrated on 1 December, is a national holiday in Romania that commemorates this event. The holiday was established after the Romanian Revolution, and commemorates the unification not only of Transylvania, but also of Bessarabia and Bukovina and parts of Banat, Crișana and Maramureș with the Romanian Kingdom. Bessarabia and Bukovina had joined with the Kingdom of Romania earlier in 1918.
Alba Iulia National Assembly.
On December 1, 1918 (N.S., November 18 O.S.), the National Assembly of Romanians of Transylvania and Hungary, consisting of 1,228 elected representatives of Romanians in Transylvania, Banat, Crișana and Maramureș, convened in Alba Iulia and decreed (by unanimous vote):
The declaration included 26 counties of the Kingdom of Hungary.
The Resolution voted by the National Assembly stipulated also the "fundamental principles for the foundation of the new Romanian State":
The union was conditional, and demanded the preservation of a democratic local autonomy, the equality of all nationalities and religions.
The Assembly also formed from 200 of its members, plus 50 co-opted members a "High National Romanian Council of Transylvania", the new permanent parliament of Transylvania.
The next day, on 2 December 1918 the High National Romanian Council of Transylvania formed a government under the name of Directory Council of Transylvania ("Consiliul Dirigent al Transilvaniei"), headed by Iuliu Maniu.
On December 11, 1918, King Ferdinand signed the Law regarding the Union of Transylvania, Banat, Crișana, the Satmar and Maramureș with the Old Kingdom of Romania, decreeing that:
Aftermath.
Versailles Treaty.
In 1920, by the Treaty of Trianon, of the Kingdom of Hungary became part of the Kingdom of Romania. This territory was smaller than that promised by the Treaty of Bucharest or claimed by the declaration of union in 1918, or demanded officially by the Romanian Government in the peace conference.
The treaty is now commemorated in Romania since 2020 as the Trianon Treaty Day.