Romania, Czechoslovakia, and Yugoslavia formed the Little Entente under French influence during the interwar years to act as a counterweight against the possible resurgence of German influence in southeastern and central Europe during the 1920s and 1930s. Romania continued to look to France to guarantee its security, at least until Britain and France sacrificed Czechoslovakia's territorial integrity in the Munich Agreement of September 1938. After Munich, French guarantees meant little, and Romania accommodated the reality of German hegemony in the region.

The Nazi-Soviet Nonaggression Pact of August 1939 squeezed Romania between the territorial ambitions of Germany and the Soviet Union. Beginning in 1940, Germany forced Romania to cede territory to Hungary, Bulgaria, and the Soviet Union (see Greater Romania to the End of World War I, 1920-45 , ch. 1). In September German forces occupied Romanian territory under the pretext of protecting the country's oil resources, access to which had already been secured in a 1939 commercial agreement. In November 1940, Romania joined Germany, Italy, and Japan in the Anti-Comintern Pact and became Hitler's base of operations to conquer the Balkans.

On June 22, 1941, Romania's third and fourth armies, a total of thirty divisions, joined Operation Barbarossa, Hitler's attack on the Soviet Union. Its forces were by far the largest and possibly the best of the fifty divisions allied with the Wehrmacht (German armed forces) on the eastern front. Romania joined the war largely in the hope of regaining northern Bukovina and Bessarabia, establishing a greater Romania at the Soviet Union's expense along the northern Black Sea coast, and also because it was simply too weak to resist Germany.

The third and fourth armies fought at Odessa and Sevastopol but became bogged down with a German army group in front of Stalingrad in October 1942. In November the Red Army counteroffensive at Stalingrad focused on encircling the powerful German Sixth Army by striking its flanks held by the relatively weaker Romanian armies. Northeast of Stalingrad, three Soviet armies punched through the Romanian Third Army and its spearhead, the Romanian First Armored Division. Southwest of Stalingrad, two Soviet armies smashed the Sixth Corps and the Eighteenth Infantry Division, the strongest elements of the Romanian Army. By November 23, the Soviet armies completed their encirclement of the German Sixth Army. In bearing the brunt of the Red Army's breakthrough at Stalingrad, nineteen Romanian divisions were badly mauled, and more than 250,000 Romanian soldiers were killed, wounded, captured, or missing in action. In August 1943, the war reached Romanian soil dramatically: 178 B-24 bombers from the United States Army's eighth and ninth air forces conducted a bombing raid from North African airfields against the oil fields at Ploiesti, a major source of fuel for the Wehrmacht. The raid reduced Romanian oil production by half and destroyed much of the country's military induf42 dustry.

The Red Army refocused its strategic attention on Romania in mid-1944. It sought to occupy Romania, knock it out of the war, and from there advance across the Danube Delta through the Carpathian Mountains into Yugoslavia and Hungary before wheeling north to roll up the right flank of Nazi Germany. Having penetrated northern Bukovina at the end of 1943, the Red Army launched the IasiKishinev Operation in August 1944 by sending eight armies with more than 1 million men across the Prut River along two convergent axes from Iasi and Kishinev in Bessarabia to drive through the Focsani Gap to capture the Ploiesti oil fields and Bucharest. Soviet armies driving from Kishinev pinned down the remnants of the German Sixth Army and seven divisions of Romania's Third Army on the Black Sea coast. Meanwhile, the bulk of Soviet forces driving from Iasi encircled the German Eighth Army and the remaining fourteen divisions of the Romanian Fourth Army. On the first day of the operation, Red Army forces destroyed five divisions of the Fourth Army in fighting northwest of Iasi. Remaining Romanian divisions simply disintegrated as their troops deserted the front.

After the August 23, 1944, coup d'état against military dictator General Ion Antonescu, King Michael arranged Romania's surrender to the Red Army. The following day, Hitler ordered 150 German bombers to attack Bucharest in a vain attempt to force Romania to rejoin the war. Romania then declared war on Germany and put its scattered forces under the command of the Red Army. These forces included parts of the Fourth Army the four divisions of the First Army, which guarded the disputed Romanian-Hungarian border during the war and the Tudor Vladimirescu First Volunteer Division, a force recruited by the Red Army from Romanian prisoners of war taken at Stalingrad who were willing to submit to communist indoctrination. These forces helped to liberate Bucharest and clear German forces from the rest of Romania, and they finished the war fighting alongside the Red Army in Hungary and Czechoslovakia. In all, Romania suffered an estimated 600,000 casualties during World War II.

Under the terms of the September 1944 armistice signed in Moscow, Romania accepted Red Army occupation of the country at least until peace negotiations commenced, agreed to pay US$300 million in war reparations, and put its oil production, rolling stock, and merchant fleet at the Soviet Union's disposal. Given the situation on the ground, the Soviet Union dominated the Allied Control Commission, which administered Romania for three years after the war. The Soviet Union also retained the right to maintain its occupation of Romania in order to keep open its lines of communication to Soviet forces occupying Austria. Under the 1947 peace treaty, Romania permanently surrendered large tracts to Bulgaria and the Soviet Union (see Armistice Negotiations and Soviet Occupation , ch. 1).

Data as of July 1989