Prior to World War I, Carol I emphasized military ties with Germany and forced France to compete with Germany as a source of military assistance for, and influence on, the Romanian state. The sympathies of most Romanians, however, lay with France. In 1913 Romania mobilized nearly 500,000 men against Bulgaria during the Second Balkan War and, at a decisive moment, marched virtually unopposed on the Bulgarian capital, Sofia.

Although it sympathized with France, Britain, and Russia, Romania maintained an armed neutrality during the first two years of World War I. The warring alliances tried to induce Romania to enter the war on their side in return for territorial gain. The Central Powers offered Bukovina and Bessarabia, which would be carved out of tsarist Russia. The Triple Entente promised Romania Transylvania, which would be detached from the Austro-Hungarian Empire.

Romania finally joined the Entente in August 1916 and fought alongside Russian armies on the eastern front. It mobilized approximately 750,000 men against German and Austro-Hungarian soldiers in the northern Carpathian Mountains and against German and Bulgarian troops along its southern border. Romanian forces suffered a string of early and catastrophic defeats, and Bucharest was occupied in December 1916. The final blow to the Romanian effort in the war was the collapse of Russian armies in October 1917, which disrupted Romania's supply lines. As a result, Romania was obliged to sue for peace in December 1917. Romania lost approximately 400,000 soldiers to combat wounds or disease, as well as untold numbers of civilians.

Although Romania was a defeated power, its French and British allies eventually were victorious, and it reaped major territorial gains as a result of the peace treaties that officially ended World War I. It received Transylvania from Austria-Hungary, Dobruja from Bulgaria, and Bukovina and Bessarabia from Soviet Russia (see fig. 1). These gains nearly doubled its size but also earned it the enmity of its immediate neighbors.

Data as of July 1989