Between 28 June and 3 July 1940, the Soviet Union occupied Bessarabia, Northern Bukovina and the Hertsa region, following an ultimatum made to Romania on 26 June 1940 that threatened the use of force. Those regions, with a total area of and a population of 3,776,309 inhabitants, were incorporated into the Soviet Union. On 26 October 1940, six Romanian islands on the Chilia branch of the Danube, with an area of , were also occupied by the Soviet Army.
The Soviet Union had planned to accomplish the annexation with a full-scale invasion, but the Romanian government, responding to the Soviet ultimatum delivered on 26 June, agreed to withdraw from the territories to avoid a military conflict. The use of force had been made illegal by the Conventions for the Definition of Aggression in July 1933, but from an international legal standpoint, the new status of the annexed territories was eventually based on a formal agreement through which Romania consented to the retrocession of Bessarabia and cession of Northern Bukovina. As it was not mentioned in the ultimatum, the annexation of the Hertsa region was not consented to by Romania, and the same is true of the subsequent Soviet occupation of the Danube islands. On 24 June, Nazi Germany, which had acknowledged the Soviet interest in Bessarabia in a secret protocol to the 1939 Molotov–Ribbentrop Pact, had been made aware prior to the planned ultimatum but did not inform the Romanian authorities and was unwilling to provide support.Bossy, G.H., Bossy, M-A. Recollections of a Romanian Diplomat, 1918–1969, Volume 2, Hoover Press, 2003. On 22 June, France, a guarantor of Romanian borders, fell to Nazi advances. This is considered to be an important factor in the Soviets' decision to issue the ultimatum.Joseph Rothschild, East Central Europe between the two World Wars University of Washington Press, Seattle, 1977; , p.314 The Soviet invasion of Bukovina in 1940 violated the Molotov-Ribbentrop Pact, since it went beyond the Soviet sphere of influence that had been agreed with the Axis.Brackman, Roman The Secret File of Joseph Stalin: A Hidden Life (2001) p. 341
On 2 August 1940, the Moldavian Soviet Socialist Republic was proclaimed as a constituent republic of the Soviet Union, encompassing most of Bessarabia and part of the Moldavian Autonomous Soviet Socialist Republic, an autonomous republic of the Ukrainian Soviet Socialist Republic on the left bank of the Dniester (now the breakaway Transnistria). The Hertsa region and the regions inhabited by Slavic majorities (Northern Bukovina, Northern and Southern Bessarabia) were included in the Ukrainian SSR. A period of political persecution, including executions, deportations to labour camps and arrests, occurred during the Soviet administration.
In July 1941, Romanian and German troops occupied Bessarabia, Northern Bukovina and Hertsa during the Axis invasion of the Soviet Union. A military administration was established, and the region's Jewish population was executed on the spot or deported to Transnistria, where large numbers were killed. In August 1944, during the Soviet Second Jassy–Kishinev Offensive, the Axis war effort on the Eastern Front collapsed. The coup of 23 August 1944 caused the Romanian army to cease resisting the Soviet advance and to join the fight against Germany. Soviet forces advanced from Bessarabia into Romania, captured much of its standing army as prisoners-of-war and occupied the country. On 12 September 1944, Romania signed the Moscow Armistice with the Allies. The Armistice and the subsequent peace treaty of 1947 confirmed the Soviet-Romanian border as it was on 1 January 1941.United States Department of State. Foreign relations of the United States, 1946. Paris Peace Conference: documents Volume IV (1946)
Bessarabia, Northern Bukovina and Hertsa remained part of the Soviet Union until it collapsed in 1991, when they became part of the newly independent states of Moldova and Ukraine. The Declaration of Independence of Moldova of 27 August 1991 declared the Soviet occupation illegal.
Background
As a historical region, Bessarabia was the eastern part of the Principality of Moldavia. In 1812, under the terms of the Treaty of Bucharest, the region was ceded by the Ottoman Empire, to which Moldavia was a vassal state, to the Russian Empire.
Interwar Soviet-Romanian relations
The Bessarabian question was both political and national in nature. According to the 1897 census, Bessarabia, then a guberniya of the Russian Empire, had a population that was 47.6% Romanians, 19.6% Ukrainians, 8% Russians, 11.8% Jews, 5.3% Bulgarians, 3.1% Germans and 2.9% Gagauz.История Республики Молдова. С древнейших времён до наших дней = Istoria Republicii Moldova: din cele mai vechi timpuri pină în zilele noastre / Ассоциация учёных Молдовы им. Н. Милеску-Спэтару — изд. 2-е, переработанное и дополненное. — Кишинёв: Elan Poligraf, 2002. — С. 146. — 360 с. — . The figures showed a strong decrease in the proportion of Moldovans and Romanians compared to the census of 1817, which had been conducted shortly after the Russian Empire annexed Bessarabia in 1812. In that survey, Moldovans and Romanians represented 86% of the population.Keith Hitchins, Rumania: 1866–1947 (Oxford History of Modern Europe). 1994, Clarendon Press. The decrease seen in the census of 1897 was caused by the Russian policies of settling of other nationalities and of Russification in Bessarabia.
During the 1917 Russian Revolution, a national assembly was formed in Bessarabia to manage the province. The assembly, known locally as Sfatul Țării, initiated several national and social reforms, and on 2/15 December 1917, it declared the Moldavian Democratic Republic an autonomous republic within the Russian Federative Democratic Republic.
The Rumcherod, an Odessa-based soviet council, loyal to the Petrograd Soviet and formed by late December, decided to take actions against the authority of Sfatul Țării. Its Front Section (Frontotdel), made up of Bolsheviks was sent to Chisinau and on 1/14 January 1918 it captured strategic locations and buildings. The Bolsheviks attempted to take power for themselves by arresting elected deputies, abolishing the Sfatul Țării and replacing it with a self-proclaimed Moldavian Soviet. None of its members were ethnic Moldavian, in contrast with Sfatul Țării where the ethnic Moldovans were about 70%. With the consent of the Allies and based on calls from more sources for a Romanian military intervention, Romanian troops entered Bessarabia in early January 1918 and, by February, had pushed the Soviets over the Dniester. In the wake of the intervention, Soviet Russia broke off diplomatic relations with Romania and confiscated the Romanian Treasure, which was stored in Moscow for safekeeping. To calm the situation, Entente representatives in Iași issued a guarantee that the presence of the Romanian Army was only a temporary military measure for the stabilisation of the front, without further affecting the political life of the region. In January 1918, the Ukrainian People's Republic declared its independence from Russia, which left Bessarabia physically isolated from the Petrograd government and led to the declaration of independence of the Moldavian Republic on 24 January/5 February. Following several Soviet protests, on 20 February/5 March, the Romanian prime minister, General Alexandru Averescu, signed a treaty with the Soviet representative in Odessa, Christian Rakovsky, which provided that Romanian troops be evacuated from Bessarabia within two months in exchange for the repatriation of Romanian prisoners-of-war held by the Rumcherod. After the White Army forced the Soviets to withdraw from Odessa, and the German Empire agreed to the Romanian annexation of Bessarabia in a secret agreement (part of the Buftea Peace Treaty) on 5/18 March,Wim P. van Meurs, The Bessarabian question in communist historiography, East European Monographs, 1994, p. 67 Romanian diplomacy repudiated the treaty by claiming that the Soviets were unable to fulfill their obligations.
On 27 March/9 April 1918, the Sfatul Țării voted for the Union of Bessarabia with Romania, conditional upon the fulfilment of an agrarian reform. There were 86 votes for union, 3 votes against, 36 deputies abstaining, and 13 deputies absent. The vote is regarded as controversial by several historians, including Romanian ones such as Cristina Petrescu and Sorin Alexandrescu.Cristina Petrescu, "Contrasting/Conflicting Identities:Bessarabians, Romanians, Moldovans" in Nation-Building and Contested Identities, Polirom, 2001, p. 156 On 18 April Georgy Chicherin, the Soviet Commissar for Foreign Affairs, sent a note of protest against the incorporation of Bessarabia into Romania.
Back in August 1916, the Entente and the neutral Romania signed a secret convention that stipulated Romania would join the war against the Central Powers in exchange for several territories of Austria-Hungary, such as Bukovina. During the end of World War I, national movements of the Romanians and the Ukrainians began to emerge in the province, but both movements had conflicting aims, each seeking to unite the province with their national state. Thus, on 25 October 1918, a Ukrainian National Committee, gaining the upper hand in Czernowitz, declared Northern Bukovina, populated by a Ukrainian majority, part of the West Ukrainian People's Republic. On 27 October the Romanians followed suit, proclaiming the whole region united with Romania, and calling in Romanian troops. The Romanian intervention quickly established the Romanian Assembly as the dominant force, and on 28 November, a Congress of the Romanians, Germans, and Poles voted to unite with Romania. The representatives of the Ukrainian and Jewish populations boycotted the Congress, and the struggle between ethnic factions continued for several months.
During the Russian Civil War, the Soviet governments of Ukraine and Russia, prompted by the unrest in Bessarabia from the Romanian occupation, issued a joint ultimatum to Romania on 1 May 1919, for its withdrawal from Bessarabia, and the next day, Christian Rakovsky, the chairman of the Ukrainian Soviet government, issued another ultimatum for the withdrawal of Romanian troops from Bukovina as well. The Red Army pushed the Romanians over the Dniester, and a Bessarabian Soviet Socialist Republic was proclaimed. The ultimatum also came in the context of the Hungarian Soviet Republic, with the Soviets hoping to prevent a Romanian intervention in Hungary. A massive rebellion in Ukraine prevented further Soviet advances.Richard K. Debo, Survival and Consolidation: The Foreign Policy of Soviet Russia, 1918–1921, McGill-Queen's Press, 1992, , pp. 113–114. Soviet Russia would continue its policy of non-recognition of Romanian sovereignty over Bessarabia, which it considered Romanian-occupied territory, until 1940.
During the negotiations before the Treaty of Paris, the United States' representative asked for a plebiscite to be held in Bessarabia to decide its future, but the proposal was rejected by the head of the Romanian delegation, Ion I. C. Brătianu, who claimed such an undertaking would allow the distribution of Bolshevik propaganda in Bessarabia and Romania. A plebiscite was also requested at the Peace Conference by the White Russians, only to be rejected again. The Soviets would continue to press for a plebiscite during the following decade, only to be dismissed every time by the Romanian government.