The United Principalities of Moldavia and Wallachia (later named Romania) is formed as a personal union under the rule of Domnitor Alexandru Ioan Cuza.

The United Principalities of Moldavia and Wallachia, 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 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, the core of the Romanian nation state.

Alexandru Ioan Cuza was the first domnitor (prince) of the Romanian Principalities through his double election as Prince of Moldavia on 5 January 1859 and Prince of Wallachia on 24 January 1859, which resulted in the unification of the two states. He was a prominent figure of the Moldavian Revolution of 1848. Following his double election, he initiated a series of liberal and progressive reforms that contributed to the modernization of Romanian society and of state structures.