United Principalities of Moldavia and Wallachia in the context of "Moldova"

The unification of Moldavia and Wallachia (Romanian: Unirea Moldovei și Țării Românești), also known as the unification of the Romanian Principalities (Romanian: Unirea Principatelor Române) or as the Little Union (Romanian: Mica Unire), happened in 1859 following the election of Alexandru Ioan Cuza as prince of both the Principality of Moldavia and the Principality of Wallachia. A potential unification between the two principalities, which shared a common Romanian ethnicity, language, and culture, had not been favored by the great powers for a long time, although it was accepted by them once it happened. The unification of these two states began a political struggle in the new country (the United Principalities of Moldavia and Wallachia) to find out which of the two regions would obtain "supremacy" and met some opposition in Moldavia by the so-called "separatists".

Nowadays, in Romania, the unification of Moldavia and Wallachia is regarded as a prelude to the Great Union, a name used in Romanian historiography to refer to the unifications of Romania with the regions of Bessarabia, Bukovina, and Transylvania in 1918 during or following the end of World War I. It is also commemorated every 24 January through the Day of the Unification of the Romanian Principalities in both Romania and Moldova.

Alexandru Ioan Cuza (Romanian: [alekˈsandru iˈo̯aŋ ˈkuza] , or Alexandru Ioan I, also Anglicised as Alexander John Cuza; 20 March [O.S. 8 March] 1820 – 15 May 1873) 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.

As ruler of the Romanian Principalities, he supported a political and diplomatic activity for the recognition of the union of Moldavia and Wallachia by the suzerain Ottoman Empire and achieved constitutional and administrative unity between Moldavia and Wallachia in 1862, when the Romanian Principalities officially adopted the name Romanian United Principalities with a single capital at Bucharest, a single national assembly and a single government.

The Romanian Old Kingdom (Romanian: Vechiul Regat or just Regat; German: Regat or Altreich) is a colloquial term referring to the territory covered by the first independent Romanian nation state, which was composed of the Romanian Principalities: Wallachia and Moldavia. The union of the two principalities was achieved when, under the auspices of the Treaty of Paris (1856), the ad hoc Divans of both countries, which were then under Ottoman Empire suzerainty, voted for Alexander Ioan Cuza as their prince. This process achieved a de facto unification under the name of the United Principalities of Moldavia and Wallachia. The region itself is defined by the result of that political act, followed by the Romanian War of Independence, the inclusion of Northern Dobruja and the transfer of the southern part of Bessarabia to the Russian Empire in 1878, the proclamation of the Kingdom of Romania in 1881, and the annexation of Southern Dobruja in 1913.

The term came into use after World War I, when the Old Kingdom became Greater Romania, after including Transylvania, Banat, Bessarabia, and Bukovina. The term now has mainly a historical relevance and is otherwise used as a common term for all regions in Romania included in both the Old Kingdom and the present borders (Wallachia, Moldavia, and Northern Dobruja).

The Russo-Turkish War (1877–1878) was a conflict between the Ottoman Empire and a coalition led by the Russian Empire which included Romania, Serbia, and Montenegro. Precipitating factors included the Russian goals of recovering territorial losses endured during the Crimean War of 1853–1856, re-establishing itself in the Black Sea and supporting the political movement attempting to free Balkan nations from the Ottoman Empire. In Romania the war is called the Russo-Romanian-Turkish War (1877–1878) or the Romanian War of Independence (1877–1878).

The Russian-led coalition won the war, pushing the Ottomans back all the way to the gates of Constantinople, leading to the intervention of the Western European great powers. As a result, Russia succeeded in claiming provinces in the Caucasus, namely Kars and Batum, and also annexed the Budjak region. The principalities of Romania, Serbia, and Montenegro, each of which had had de facto sovereignty for some years, formally proclaimed independence from the Ottoman Empire. After almost five centuries of Ottoman domination (1396–1878), Bulgaria emerged as an autonomous state with support and military intervention from Russia.