Michael I of Romania in the context of "Great Union Day"

Romania is a country located at the crossroads of Central, Eastern and Southeast Europe. It borders Ukraine to the north and east, Hungary to the west, Serbia to the southwest, Bulgaria to the south, Moldova to the east, and the Black Sea to the southeast. It has a mainly continental climate, and an area of 238,397 km (92,046 sq mi) with a population of 19 million people. Romania is the twelfth-largest country in Europe and the sixth-most populous member state of the European Union. Europe's second-longest river, the Danube, empties into the Danube Delta in the southeast of the country. The Carpathian Mountains cross Romania from the north to the southwest and include Moldoveanu Peak, at an altitude of 2,544 m (8,346 ft). Bucharest is the country's capital, largest urban area, and financial centre. Other major urban areas include Cluj-Napoca, Timișoara, Iași, Constanța and Brașov.

Settlement in the territory of modern Romania began in the Lower Paleolithic, later becoming the Dacian Kingdom before Roman conquest and Romanisation. The modern Romanian state was formed in 1859 with the unification of Moldavia and Wallachia under Alexandru Ioan Cuza, becoming the Kingdom of Romania in 1881 under Carol I of Romania. Romania gained independence from the Ottoman Empire in 1877, formalised by the Treaty of Berlin. After World War I, Transylvania, Banat, Bukovina, and Bessarabia joined the Old Kingdom, forming Greater Romania, which reached its largest territorial extent. In 1940, under Axis pressure, Romania lost territories to Hungary, Bulgaria, and the Soviet Union. Following the 1944 Romanian coup d'état, Romania switched sides to join the Allies. After World War II, it regained Northern Transylvania through the Paris Peace Treaties. Under Soviet occupation, King Michael I was forced to abdicate, and Romania became a socialist republic and Warsaw Pact member. After the uniquely violent Romanian revolution in December 1989, Romania began a transition to liberal democracy and a market economy.

The Kingdom of Romania (Romanian: Regatul României) was a constitutional monarchy that existed from 25 March [O.S. 13 March] 1881 with the crowning of prince Karl of Hohenzollern-Sigmaringen as King Carol I (thus beginning the Romanian royal family), until 1947 with the abdication of King Michael I and the Romanian parliament's proclamation of the Romanian People's Republic.

From 1859 to 1877, Romania evolved from a personal union of two principalities: (Moldavia and Wallachia) called the Unification of Moldavia and Wallachia also known as "The Little Union" under a single prince to an autonomous principality with a Hohenzollern monarchy. The country gained its independence from the Ottoman Empire during the 1877–1878 Russo-Turkish War (known locally as the Romanian War of Independence), after which it was forced to cede the southern part of Bessarabia in exchange for Northern Dobruja. The kingdom's territory during the reign of King Carol I, between 13 (O.S.) / 25 March 1881 and 27 September (O.S.) / 10 October 1914 is sometimes referred to as the Romanian Old Kingdom, to distinguish it from "Greater Romania", which included the provinces that became part of the state after World War I (Bessarabia, Banat, Bukovina, and Transylvania).

The 1944 Romanian coup d'état, better known in Romanian historiography as the Act of 23 August (Romanian: Actul de la 23 august), was a coup d'état led by King Michael I of Romania during World War II on 23 August 1944. With the support of several political parties, the king removed the government of Ion Antonescu, which had aligned Romania with Nazi Germany, after the Axis front in northeastern Romania collapsed in the face of a successful Soviet offensive. The Romanian Army declared a unilateral ceasefire with the Soviet Red Army on the Moldavian front, an event viewed as decisive in the Allied advances against the Axis powers in the European theatre of World War II. The coup was supported by the Romanian Communist Party, the Social Democratic Party, the National Liberal Party, and the National Peasants' Party who had coalesced into the National Democratic Bloc in June 1944.

The Soviet occupation of Romania refers to the period from 1944 to August 1958, during which the Soviet Union maintained a significant military presence in Romania. The fate of the territories held by Romania after 1918 that were incorporated into the Soviet Union in 1940 is treated separately in the article on Soviet occupation of Bessarabia and Northern Bukovina.

During the Eastern Front offensive of 1944, the Soviet Army occupied the northwestern part of Moldavia as a result of armed combat that took place between the months of April and August of that year, while Romania was still an ally of Nazi Germany. The rest of the territory was occupied after Romania changed sides in World War II, as a result of the royal coup launched by King Michael I on August 23, 1944. On that date, the king announced that Romania had unilaterally ceased all military actions against the Allies, accepted the Allied armistice offer, and joined the war against the Axis powers. As no formal armistice offer had been extended yet, the Red Army occupied most of Romania as enemy territory prior to the signing of the Moscow Armistice of September 12, 1944.

The Socialist Republic of Romania (Romanian: Republica Socialistă România, RSR) was a communist state that existed officially in Romania from 1947 to 1989 (see Revolutions of 1989). From 1947 to 1965, the state was known as the Romanian People's Republic (Republica Populară Romînă, RPR). The country was an Eastern Bloc state and a member of the Warsaw Pact with a dominant role for the Romanian Communist Party enshrined in its constitutions. Geographically, RSR was bordered by the Black Sea to the east, the Soviet Union (via the Ukrainian and Moldavian SSRs) to the north and east, Hungary and Yugoslavia (via SR Serbia) to the west, and Bulgaria to the south.

As World War II ended, Romania, a former Axis member which had overthrown their pro-Axis government, was occupied by the Soviet Union as the sole representative of the Allies. On 6 March 1945, after mass demonstrations by communist sympathizers and political pressure from the Soviet representative of the Allied Control Commission, a new pro-Soviet government that included members of the previously outlawed Romanian Workers' Party was installed. Gradually, more members of the Workers' Party and communist-aligned parties gained control of the administration and pre-war political leaders were steadily eliminated from political life. In December 1947, King Michael I was forced to abdicate and the People's Republic of Romania was declared.

The King of Romania (Romanian: Regele României) or King of the Romanians (Romanian: Regele Românilor) was the title of the monarch of the Kingdom of Romania from 1881 until 1947, when the Romanian Workers' Party proclaimed the Romanian People's Republic following Michael I's forced abdication.

The Romanian royal family (Romanian: Familia regală a României) constitutes the Romanian subbranch of the Swabian branch of the House of Hohenzollern (also known as the House of Hohenzollern-Sigmaringen), and was the ruling dynasty of the Kingdom of Romania, a constitutional monarchy in Central-Eastern Europe. The kingdom existed from 1881, when Carol I was proclaimed king, until 1947, when the last king, Michael I, was forced to abdicate and the Parliament proclaimed Romania a republic. Soon after, upon the establishment of the constitution of 13 April 1948, Romania became a people's republic, a state that lasted until the Romanian Revolution in 1989.

Current members of the former royal family include the daughters of the late, former King Michael of Romania. Some descendants have adopted the surname "of Romania". There are also descendants of Michael's older half-brother Carol Lambrino (also known as "Carol Hohenzollern" and "Carol Mircea Grigore of Romania" or, in Romanian, al României, on his amended, Romanian birth certificate), whose legitimacy was disputed and who were not recognised as royal during the reigns of Ferdinand, Carol II and Michael.

The Romanian Communist Party (Romanian: Partidul Comunist Român [parˈtidul komuˈnist roˈmɨn]; PCR) was a communist party in Romania. Founded in 1921, the party assumed to the power of Romania in 1947 and became the founding and ruling party of the Socialist Republic of Romania, until its overthrow in the Romanian revolution in 1989. Ideologically committed to Marxism–Leninism, the party oversaw Romania's departure from the Soviet satellite status and incorporation of national communism.

The successor to the pro-Bolshevik wing of the Socialist Party of Romania, it gave an ideological endorsement to a communist revolution that would replace the social system of the Kingdom of Romania. After being outlawed in 1924, the PCR remained a minor and illegal grouping for much of the interwar period and submitted to direct Comintern control. During the 1920s and the 1930s, most of its activists were imprisoned or took refuge in the Soviet Union, which led to the creation of competing factions that sometimes came into open conflict. That did not prevent the party from participating in the political life of the country through various front organizations, most notably the Peasant Workers' Bloc. In 1934–1936, PCR reformed itself in the mainland of Romania properly, with foreign observers predicting a possible communist takeover in Romania. The party emerged as a powerful actor on the Romanian political scene in August 1944, when it became involved in the royal coup that toppled the pro-Nazi government of Ion Antonescu. With support from Soviet occupational forces, the PCR pressured King Michael I into abdicating, and it established the Romanian People's Republic in December 1947.

Gheorghe Gheorghiu-Dej (Romanian pronunciation: [ˈɡe̯orɡe ɡe̯orˈɡi.u ˈdeʒ] 8 November [O.S. 26 October] 1901 – 19 March 1965) was a Romanian politician. He was the first communist leader of Romania from 1947 to 1965, serving as first secretary of the Romanian Communist Party (ultimately "Romanian Workers' Party", PMR) from 1944 to 1954 and from 1955 to 1965, and as the first communist Prime Minister of Romania from 1952 to 1955.

Born in Bârlad (1901), Gheorghiu-Dej was involved in the communist movement's activities from the early 1930s. Upon the outbreak of World War II in Europe, he was imprisoned by Ion Antonescu's regime in the Târgu Jiu internment camp, and escaped only in August 1944. After the forces of King Michael ousted Antonescu and had him arrested for war crimes, Gheorghiu-Dej together with prime-minister Petru Groza pressured the King into abdicating in December 1947, marking the onset of out-and-out communist rule in Romania.