Romania occupies 238,397 square kilometers in southeastern Europe where the Carpathian Mountains form a horseshoe across the center of the country and the Danube River marks 1,075 kilometers of its southern border before emptying into a 5,800-square-kilometer delta on the Black Sea coast. This geography creates what amounts to three concentric zones: the arc of mountains, the plateau of Transylvania enclosed within that arc, and the outer plains of Wallachia to the south, Moldavia to the east, and smaller historic regions including Banat and Dobruja. The configuration concentrates biodiversity in a compact area. The Danube Delta Biosphere Reserve hosts 325 bird species during migration cycles and contains the largest continuous wetland in Europe outside Russia. Retezat National Park in the Southern Carpathians holds more than 1,190 plant species including 90 endemic to the Carpathians. Bears' Cave near Chișcău preserves skeletal remains of Ursus spelaeus in calcite formations dating to the Pleistocene. The Apuseni Natural Park contains over 400 caves including Scărișoara Ice Cave where an underground glacier has persisted for approximately 3,500 years according to carbon dating of organic material trapped in ice layers.
The Carpathian Mountains themselves split into three sections. The Eastern Carpathians run from the Ukrainian border south roughly 600 kilometers. The Southern Carpathians, also called Transylvanian Alps, continue west for approximately 250 kilometers and contain Moldoveanu Peak at 2,544 meters, the country's highest point. The Western Carpathians arc north to close the ring. This structure isolates Transylvania from surrounding regions enough that medieval trade routes required passage through specific gaps where towns like Brașov grew wealthy controlling access. The Iron Gates gorge where the Danube cuts between the Carpathians and the Balkan range creates the narrowest point on the lower Danube, now widened by a joint Romanian-Yugoslav dam project completed in 1972 that raised water levels by 35 meters and created a reservoir extending 150 kilometers upstream.
Romania entered written record through Greek colonies on the Black Sea coast in the 7th century BCE including Histria, Tomis, and Callatis. The Romans conquered Dacia under Emperor Trajan between 101 and 106 CE, establishing the province that gives modern Romania its name and Romance language. Roman withdrawal in 271 CE left a population speaking a Latin-derived language isolated from other Romance regions by incoming Slavic peoples. This linguistic island persisted through successive migrations of Goths, Huns, Avars, Bulgars, Hungarians, Pechenegs, Cumans, and Mongols. The medieval period produced three principalities: Wallachia south of the Carpathians, Moldavia to the east, and Transylvania within the mountain arc. Wallachia achieved autonomy from Hungarian suzerainty in 1330 under Basarab I. Moldavia emerged as a distinct principality in 1359 under Bogdan I. Transylvania remained under Hungarian then Habsburg control until 1918.
Ottoman suzerainty over Wallachia and Moldavia began in the 15th century but differed from administration in territories further south. The principalities retained native rulers, Orthodox Christianity, and internal autonomy while paying tribute and providing troops. This arrangement persisted with interruptions until Russian military intervention in 1828-29 resulted in the Treaty of Adrianople establishing Russian protectorate status. The Crimean War shifted European power balances. The Congress of Paris in 1856 placed the principalities under collective European guarantee. Moldavia and Wallachia elected Alexandru Ioan Cuza as ruler in separate votes in January and February 1859, creating a personal union the Ottoman Empire recognized in 1861 and formalized as Romania in 1862. Cuza secularized monastery lands comprising approximately 25 percent of arable territory in 1863 and initiated land reform before a coup removed him in 1866. Carol I of Hohenzollern-Sigmaringen became prince, then king after independence was declared in 1877 during the Russo-Turkish War and recognized at the Congress of Berlin in 1878.
World War I offered territorial expansion. Romania entered the war in August 1916 on the Allied side with explicit aims to acquire Transylvania, Bukovina, and Banat from Austria-Hungary. Initial advances into Transylvania reversed within months. German and Austro-Hungarian forces occupied Bucharest in December 1916. The Treaty of Bucharest in May 1918 imposed harsh terms on defeated Romania. The November 1918 collapse of Austria-Hungary and Germany's defeat reversed outcomes. Transylvania, Bessarabia, Bukovina, and parts of Banat unified with Romania between November 1918 and April 1920, creating Greater Romania with territory expanded from approximately 137,000 to 295,000 square kilometers and population increased from 7.5 million to over 18 million. The 1930 census recorded 18,057,028 inhabitants including substantial Hungarian, German, Jewish, Ukrainian, Russian, Bulgarian, Turkish, and Roma minorities.
World War II dismembered Greater Romania before military action began. The Soviet Union annexed Bessarabia and Northern Bukovina in June 1940 under the Molotov-Ribbentrop Pact. The Second Vienna Award in August 1940 transferred Northern Transylvania to Hungary. The Treaty of Craiova in September 1940 ceded Southern Dobruja to Bulgaria. Romania allied with Germany in June 1941, participating in Operation Barbarossa with aims to recover Bessarabia. Romanian forces besieged Odessa for 73 days and occupied territory east to the Dnieper including Odessa and Transnistria under Romanian administration. Romanian armies reached Stalingrad. King Michael's coup on August 23, 1944 switched Romania to the Allied side. Soviet forces occupied the country. The Paris Peace Treaty of 1947 restored Northern Transylvania but confirmed Soviet retention of Bessarabia and Northern Bukovina and Bulgarian retention of Southern Dobruja.
Communist rule consolidated between 1945 and 1947. King Michael abdicated under pressure on December 30, 1947. The Romanian People's Republic was proclaimed the same day. Gheorghe Gheorghiu-Dej led the party until his death in 1965. Nicolae Ceaușescu succeeded him and ruled until December 1989. Ceaușescu initially pursued partial independence from Moscow, refusing to participate in the 1968 Warsaw Pact invasion of Czechoslovakia and maintaining diplomatic relations with Israel after 1967 and China after the Sino-Soviet split. These positions earned Western favor. President Richard Nixon visited Bucharest in August 1969. Ceaușescu received a British knighthood in 1978, revoked posthumously in 1989. Domestic policy grew increasingly repressive. Systematization policies begun in 1974 demolished approximately 8,000 villages and urban historic centers. The plan to erase Bucharest's historic center for the House of the People, now Palace of Parliament, destroyed approximately 7 square kilometers including 19 Orthodox churches, 6 synagogues, 3 Protestant churches, and over 30,000 residences. The building consumed 700,000 tons of steel, one million cubic meters of marble, 900,000 cubic meters of wood, and 200,000 square meters of wool carpet. It ranks as the second-largest administrative building by floor area after the Pentagon, with 365,000 square meters spread across 12 stories above ground and 8 below, reaching 84 meters high.