Before World War I, the union of Michael the Brave, who ruled over the three principalities with Romanian population (Wallachia, Transylvania and Moldavia) for a short period of time,^[79] was viewed in later periods as the precursor of a modern Romania, a thesis which was argued with noted intensity by Nicolae Bălcescu. This theory became a point of reference for nationalists, as well as a catalyst for various Romanian forces to achieve a single Romanian state.^[80]

In 1918, at the end of World War I, the union of Romania with Bukovina was ratified in 1919 in the Treaty of Saint Germain,^[81] and some of the Allies recognized the union with Bessarabia in 1920 through the never ratified Treaty of Paris.^[82] On 1 December, the Deputies of the Romanians from Transylvania voted to unite Transylvania, Banat, Crișana and Maramureș with Romania by the Proclamation of Union of Alba Iulia. Romanians today celebrate this as the Great Union Day, that is a national holiday.

The Romanian expression România Mare (Great or Greater Romania) refers to the Romanian state in the interwar period and to the territory Romania covered at the time. At that time, Romania achieved its greatest territorial extent, almost 300,000 km2 or 120,000 sq mi^[83]), including all of the historic Romanian lands.^[84] Today, the concept serves as a guiding principle for the unification of Romania and Moldova.