The United Principalities of Moldavia and Wallachia, also known as The Romanian United Principalities, was the official name of Romania following the 1859 election of Alexandru Ioan Cuza as the Ruling Prince or domnitor of both territories. On 24 January (O.S.) (5 February) 1862, the Principality of Moldavia and the Principality of Wallachia formally united to create the United Principalities. Alongside Transylvania, the principalities became the core of the Romanian nation state. A new constitution came into effect in 1866 giving the country the official name Romania, and on 14 March (O.S.) (26 March) 1881, it became the Kingdom of Romania.