This is a map of the area known as Europe before the First World War. If you look at the gray area this is the Austrian Empire. This Empire would be destroyed by 1919.
Beside this grey mass is Romania. They had at this point gained independence from the Ottoman Empire in the late 1800s
This is of course during the period when Transylvania was a part of the Kingdom of Hungary and not a part of the Kingdom of Romania. In fact, at some point it was also known as the Grand Principality of Transylvania. Yet, for many people they were Romanian by origin of both culture and ethnic. The also had a different religion-- Romanian Orthodox