Hungary–Romania relations
Relations between Hungary and Romania were officially established on August 21, 1920 in the current form, but the two countries have a long mutual history dating back to the Middle Ages. Transylvania, today entirely situated within the borders of Romania, has been a subject of animosity between the two states, having previously been part of the Kingdom of Hungary for centuries.
Source: Wikipedia — Hungary–Romania relations (CC BY-SA 4.0)