Trianon Treaty Day, officially observed in Romania, is celebrated every June 4 to commemorate the signing of the Treaty of Trianon, which established the border between Romania and Hungary after World War I. The treaty, signed in Versailles in 1920, resulted in Hungary losing over two-thirds of its territory, including Transylvania, which Romania gained. This observance highlights the significance of the treaty and its impact on Romania's history, and it is marked by various cultural and educational events. The day was proposed for annual observance in 2015 and officially established by President Klaus Iohannis in 2020, with the first celebration occurring in 2021. The observance has faced controversy, particularly from Hungary and Romania's Hungarian minority, as it coincides with Hungary's National Unity Day.