During Cuza’s reign, many fundamental institutions of a modern state were created, and an important land reform took place. In 1866, Cuza abdicated and Prince Carol of Hohenzollern-Sigmaringen came to the throne. Under his reign, Romania became independent (1877), a new constitution was passed, and the country entered a period of great economic development.
Romania entered the First World War in 1916, on the Allied side. The Romanian Army fought valiantly in the summer of 1917 and registered heavy losses.
In 1918 the National Assemblies of the regions of Transylvania (to the West), Bassarabia (the territory of the present day Republic of Moldova), and Bucovina (now part of the Ukraine) decided to unite with Romania.
On the 1st of December, 1918, the great national assembly in Alba Iulia proclaimed the "unification of all Romanians from Transylvania, the Banat, Crisana and Maramures with Romania for all ages to come".
In 1990 it was decided to celebrate 1st December as Romanian National Day.
National Day history: The first National Day of Romania was set to be on May 10, which had a double meaning; it was the day on which the Romanian monarchy was instituted (in 1866), and it was the day on which the Declaration of Independence was signed (in 1877). The communist regime changed the date of the national holiday to August 23 to mark the 1944 overthrow of the fascist government.