When Did Transylvania Become a Part of Romania?

Before 1918 and the Great War, Transylvania was a part of the Kingdom of Hungary, which was itself a part of the Empire of Austria.

The question of when Transylvania became a part of the Kingdom of Romania, is far more interesting:  On December 1, 1918 a vote took place in the city of Alba Iulia (near a the ruins of its citadel). The people of Transylvania voted on that day to join with the Kingdom of Romania, so this is one possible date.

Another possible date is when the Romanian Army entered the city of Brasov and Cluj by conquest on December 7, 1918.  Perhaps this is when when Transylvania became a part of Romania.  It was not until 1919 that the fighting ceased between Romania and Hungary.  This fighting is known as the Romanian-Hungarian conflict.

King Ferdinand of Romania signed a new constitution in 1923 that dealt with Transylvania and the other territories gained after the Paris Peace conferences.  There are then several dates on which one could say Transylvania became a part of Romania.  The most accepted is in 1918 and the Paris Peace conference of 1919.