Kingdom of Romania in the context of "Unification of Moldavia and Wallachia"

The Balkan Wars were two conflicts that took place in the Balkan states in 1912 and 1913. In the First Balkan War, the four Balkan states of Greece, Serbia, Montenegro and Bulgaria declared war upon the Ottoman Empire and defeated it, in the process stripping the Ottomans of their European provinces, leaving only Eastern Thrace under Ottoman control. In the Second Balkan War, Bulgaria fought against the other four combatants of the first war. It also faced an attack from Romania from the north. The Ottoman Empire lost the bulk of its territory in Europe. Although not involved as a combatant, Austria-Hungary became relatively weaker as a much enlarged Serbia pushed for union of the South Slavic peoples. The war set the stage for the July crisis of 1914 and as a prelude to the First World War.

By the early 20th century, Bulgaria, Greece, Montenegro and Serbia had achieved independence from the Ottoman Empire, but large elements of their ethnic populations remained under Ottoman rule. Over the course of the Macedonian Struggle these states fought for influence between themselves and the Ottoman government within Ottoman Macedonia, during which their governments came under the control of nationalists. In 1912, these countries united to formed the Balkan League. The First Balkan War began on 8 October 1912, when the League member states attacked the Ottoman Empire, and ended eight months later with the signing on 30 May 1913 of the Treaty of London negotiated together with the Great Powers. The Great Powers - particularly Italy and Austria-Hungary -- included independence for Albania in the Treaty. The Second Balkan War began on 16 June 1913, when Bulgaria, dissatisfied with its allotment of territory from Macedonia, attacked its former Balkan League allies. The combined forces of the Serbian and Greek armies, with their superior numbers repelled the Bulgarian offensive and counter-attacked by invading Bulgaria from the west and the south. Romania, having taken no part in the first conflict, had intact armies to strike with and invaded Bulgaria from the north in violation of a peace treaty between the two states. The Ottoman Empire also attacked Bulgaria and advanced in Thrace, regaining Adrianople. In the resulting Treaty of Bucharest, Bulgaria managed to retain most of the territories it had gained in the First Balkan War. However, it was forced to cede the ex-Ottoman south part of Dobruja province to Romania.

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.

Between 28 June and 3 July 1940, the Soviet Union occupied Bessarabia and Northern Bukovina, following an ultimatum made to Romania on 26 June 1940 that threatened the use of force. Those regions, with a total area of 50,762 km (19,599 sq mi) 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 23.75 km (9.17 sq mi), 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. 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. 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.

The Balkans campaign of World War II began with the Italian invasion of Greece on 28 October 1940. In the early months of 1941, Italy's offensive had stalled and a Greek counter-offensive pushed into Albania. Germany sought to aid Italy by deploying troops to Romania and Bulgaria and attacking Greece from the east. Meanwhile, the British landed troops and aircraft to shore up Greek defences. A coup d'état in Yugoslavia on 27 March caused Adolf Hitler to order the conquest of that country.

The invasion of Yugoslavia by Germany and Italy began on 6 April 1941, simultaneously with the renewed invasion of Greece; on 11 April, Hungary joined the invasion of Yugoslavia. By 17 April the Yugoslavs had signed an armistice, and by 30 April all of mainland Greece was under German or Italian control. On 20 May Germany invaded Crete by air, and by 1 June all remaining Greek and British forces on the island had surrendered. Although it had not participated in the attacks in April, Bulgaria occupied parts of both Yugoslavia and Greece shortly thereafter for the remainder of the war in the Balkans.

The Tripartite Pact, also known as the Berlin Pact, was an agreement between Germany, Italy, and Japan signed in Berlin on 27 September 1940 by, respectively, Joachim von Ribbentrop, Galeazzo Ciano, and Saburō Kurusu (in that order) and in the presence of Adolf Hitler. It was a defensive military alliance that was eventually joined by Hungary (20 November 1940), Romania (23 November 1940), Slovakia (24 November 1940), Bulgaria (1 March 1941), and Yugoslavia (25 March 1941). Yugoslavia's accession provoked a coup d'état in Belgrade two days later. Germany, Italy, and Hungary responded by invading Yugoslavia. The resulting Italo-German client state, known as the Independent State of Croatia, joined the pact on 15 June 1941.

The Tripartite Pact was, together with the Anti-Comintern Pact and the Pact of Steel, one of a number of agreements between Germany, Japan, Italy, and other countries of the Axis powers governing their relationship.

The Eastern Front, also known as the Great Patriotic War in the Soviet Union and its successor states, and the German–Soviet War in modern Germany and Ukraine, was a theatre of World War II fought between the European Axis powers and Allies, including the Soviet Union (USSR) and Poland. It encompassed Central Europe, Eastern Europe, Northeast Europe (Baltics), and Southeast Europe (Balkans), and lasted from 22 June 1941 to 9 May 1945. Of the estimated 70–85 million deaths attributed to the war, around 30 million occurred on the Eastern Front, including 9 million children. The Eastern Front was decisive in determining the outcome in the European theatre of operations in World War II and is the main cause of the defeat of Nazi Germany and the Axis nations. Historian Geoffrey Roberts noted that "more than 80 percent of all combat during the Second World War took place on the Eastern Front".

The Axis forces, led by Germany, invaded the Soviet Union in Operation Barbarossa on 22 June 1941. Despite warnings and the deployment of Axis armies on his borders, Stalin refused to believe that Hitler would invade and forbade any defensive preparations. Thus the Soviets were caught completely unprepared. They were unable to halt deep Axis advances into Russia, which came close to seizing Moscow. However, the Axis failed to capture the city, and Hitler shifted his focus to the oil fields of the Caucasus the following year. German forces advanced into the Caucasus under Fall Blau ("Case Blue"), launched on 28 June 1942. The Soviets decisively defeated the Axis at the Battle of Stalingrad—the bloodiest battle in the war and arguably in all of history—making it one of the key turning points of the front. A second great Axis defeat, at the Battle of Kursk, crippled German offensive capabilities permanently and cleared the way for Soviet offensives. Several Axis allies defected to the Allies, such as Italy, Romania and Bulgaria. The Eastern Front concluded with the capture of Berlin, followed by the signing of the German Instrument of Surrender on 8 May, ending the Eastern Front and the war in Europe.

The Treaty of Lausanne (French: Traité de Lausanne, Turkish: Lozan Antlaşması) is a peace treaty negotiated during the Lausanne Conference of 1922–1923 and signed in the Palais de Rumine in Lausanne, Switzerland, on 24 July 1923. The treaty officially resolved the conflict that had initially arisen between the Ottoman Empire and the Allied French Republic, British Empire, Kingdom of Italy, Empire of Japan, Kingdom of Greece, Kingdom of Serbia, and the Kingdom of Romania since the outset of World War I. The original text of the treaty is in English and French. It emerged as a second attempt at peace after the failed and unratified Treaty of Sèvres, which had sought to partition Ottoman territories. The earlier treaty, signed in 1920, was later rejected by the Turkish National Movement which actively opposed its terms. As a result of Greek defeat in the Greco-Turkish War, Turkish forces recaptured İzmir, and the Armistice of Mudanya was signed in October 1922. This armistice provided for the exchange of Greek-Turkish populations and allowed unrestricted civilian, non-military passage through the Turkish Straits.

Turkey ratified the treaty on 23 August 1923, and all other signatories did so by 16 July 1924. The Treaty of Lausanne became effective on 6 August 1924.

Banat, Bačka, and Baranya (Serbo-Croatian: Banat, Bačka i Baranja / Банат, Бачка и Барања) was a province of the Kingdom of Serbia and the Kingdom of Serbs, Croats, and Slovenes between November 1918 and 1922. It included the geographical regions of Banat, Bačka, and Baranya and its administrative center was Novi Sad. They were later separated from the country to become SAP Vojvodina in 1945 with the creation of Federal Yugoslavia; smaller parts of Baranya were incorporated into Croatia or ceded to Kingdom of Hungary, while a portion of Banat was ceded to Kingdom of Romania.

At the Congress of Berlin (13 June – 13 July 1878), the major European powers revised the territorial and political terms imposed by the Russian Empire on the Ottoman Empire by the Treaty of San Stefano (March 1878), which had ended the Russo-Turkish War of 1877–1878. The Congress was the result of escalating tensions; particularly British opposition to Russian hegemony over the Ottoman Empire in the Balkans, through the creation of a Russian-aligned 'Greater Bulgaria'. To secure the European balance of power in favour of its splendid isolation achieved after the Crimean War, Britain stationed the Mediterranean Fleet near Constantinople to enforce British demands. To avoid war, Otto von Bismarck, Chancellor of the newly formed German Empire, was asked to mediate a solution that would restore the Ottoman Empire's position as a counterbalance to Russian influence in the Mediterranean and the Balkans, in line with the principles of the 1856 Treaty of Paris.

Attended by delegates from Europe's then six great powers: Russia, Great Britain, France, Austria-Hungary, Italy, and Germany; the Ottomans as well as representatives of four Balkan states (Greece, Serbia, Romania and Montenegro), the Congress culminated in the Treaty of Berlin (13 July 1878). This agreement essentially dismantled the autonomous Greater Bulgarian State envisaged at San Stefano, and reorganised the borders of south-eastern Europe. The main results were the Austro-Hungarian forcible occupation of Bosnia and Herzegovina, the British de facto annexation of Cyprus under false pretenses, and the formal recognition of the self-declared independence of Romania, Serbia and Montenegro; allies of Russia in the previous war. While the settlement averted war, it exacerbated nationalist grievances in the Balkans and deepened the rivalry between Britain and Russia (The Great Game), contributing to long-term regional instability that foreshadowed the Balkan Wars and World War I.

The Second Balkan War (29 June – 10 August 1913) was a conflict fought between the Kingdom of Bulgaria and its former Balkan League allies, Serbia and Greece, who were later joined by Romania and the Ottoman Empire. The war began when Bulgaria, unhappy with the division of territory after the First Balkan War, launched attacks on Serbian and Greek forces, who repelled the offensive and pushed into Bulgarian territory. With most of Bulgaria’s army committed in the south, Romania intervened from the north. The Ottoman Empire also took advantage of the situation to recover territories lost the previous year.

As Bulgaria suffered military setbacks on multiple fronts and Romanian forces advanced towards its capital, Sofia, it requested an armistice. The war ended with the Treaty of Bucharest, which compelled Bulgaria to cede significant territory: Southern Dobruja to Romania, parts of Macedonia to Serbia and Greece, and Adrianople (Edirne) to the Ottoman Empire under the separate Treaty of Constantinople.