United Principalities of Moldavia and Wallachia

The United Principalities of Moldavia and Wallachia (Romanian: Principatele Unite ale Moldovei și Țării Românești), commonly called United Principalities or Wallachia and Moldavia, was the personal union of the Principality of Moldavia and the Principality of Wallachia. The union was formed on 5 February[O.S. 24 January] 1859 when Alexandru Ioan Cuza was elected as the Domnitor (Ruling Prince) of both principalities. Their separate autonomous vassalage in the Ottoman Empire continued with the unification of both principalities. On 3 February[O.S. 22 January] 1862, Moldavia and Wallachia formally united to create the Romanian United Principalities or Romania the core of the Romanian nation state.

In February 1866, Prince Cuza was forced to abdicate and go into exile by a political coalition led by the Liberals; the German prince Karl of Hohenzollern-Sigmaringen was offered the throne and, on 22 May[O.S. 10 May] 1866 he entered Bucharest for the first time. In July the same year, a new constitution came into effect, giving the country the name of Romania; internationally, this name was used only after 1877–78, since at the time it was still nominally a vassal of the Ottoman Empire. However, by this time the suzerainty of the Sublime Porte had become a legal fiction. Romania had its own flag and anthem; after 1867, it had its own currency as well.

On 21 May[O.S. 9 May] 1877, Romania proclaimed itself fully independent; the proclamation was sanctioned by the Domnitor the following day. The Ottoman Empire finally recognized Romanian independence in the Treaty of San Stefano. Three years later, on 22 May[O.S. 10 May] 1881, the 1866 Constitution was modified and Romania became a kingdom, and Domnitor Carol I was crowned as the first king of Romania. After the First World War, Transylvaniaand other territories were also included.

For its triple symbolic meaning, the date of May 10 was celebrated as Romania's National Day until 1947, when the Communist regime installed the republic.