The Romanian state was formed in 1859 through a personal union of the Danubian Principalities of Moldavia and Wallachia. The new state, officially named Romania since 1866, gained independence from the Ottoman Empire in 1877. During World War I, after declaring its neutrality in 1914, Romania fought together with the Allied Powers from 1916. In the aftermath of the war, Bukovina, Bessarabia, Transylvania, and parts of Banat, Crișana, and Maramureș became part of the Kingdom of Romania. In June–August 1940, as a consequence of the Molotov–Ribbentrop Pact and Second Vienna Award, Romania was compelled to cede Bessarabia and Northern Bukovina to the Soviet Union and Northern Transylvania to Hungary. In November 1940, Romania signed the Tripartite Pact and, consequently, in June 1941 entered World War II on the Axis side, fighting against the Soviet Union until August 1944, when it joined the Allies and recovered Northern Transylvania.

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 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.