Romania in World War I

The Kingdom of Romania was neutral for the first two years of World War I, entering on the side of the Allied powers from 27 August 1916 until Central Power occupation led to the Treaty of Bucharest in May 1918, before reentering the war on 10 November 1918. It had the most significant oil fields in Europe, and Germany eagerly bought its petroleum, as well as food exports.

Romania in World War I
Part of the Eastern Front of World War I

Romanian troops at Mărășești battlefield in 1917.
Date27 August 1916 – December 1917; 10–11 November 1918
Location
Result

Central Powers victory

Allied victory

Belligerents
 Germany
 Austria-Hungary
 Bulgaria
 Ottoman Empire
 Romania
 Russia
 Serbia[1]
Support:
 France
Commanders and leaders
Erich von Falkenhayn
August von Mackensen
Johannes von Eben
Archduke Karl
A. A. von Straußenburg
Franz Rohr von Denta
Stefan Toshev
Mustafa Hilmi Pasha
Ferdinand I
Constantin Prezan
Alexandru Averescu
Eremia Grigorescu
Ioan Culcer
Mihail Aslan
Vladimir Sakharov
Dmitry Shcherbachev
Andrei Zayonchkovski
Milenko Milićević
Henri Berthelot
Units involved
9th Army
Danube Army
1st Army
3rd Army
VI Corps
Danube Flotilla
Constantinople Flotilla

Romanian Front

4th Army
3rd Army
Dobruja Army
1st Serbian Division
French Mission
Romanian Navy
Strength
750,000[2]
143,049 (1916)[3]
20,000 (1916)[4]
39,000 (1917)[5]

1916:[6]
658,088
30,000
20,000
1,600
1917:
400,000
1,000,000

Casualties and losses
191,000[7][8]
96,600[9][10]
30,250+[11][12][13]
20,000[14]
1 river monitor sunk
1 river monitor disabled
1 submarine sunk
1 aircraft destroyed
Total: 338,000 casualties

535,700[15]
335,706 dead
120,000 wounded
80,000 captured
50,000

9,000
3,000 dead
6,000 wounded
2 torpedo boats sunk
1 gunboat sunk
Total: 595,000 casualties
330,000–430,000 Romanian civilian dead from war-related causes between 1914 and 1918[16]

From the point of view of its belligerent status, Romania was a neutral country between 28 July 1914 and 27 August 1916, a belligerent country on the part of the Entente from 27 August 1916 to 9 December 1917, in a state of armistice with the Central Powers from 10 December 1917 to 7 May 1918, a non-combatant country between 7 May 1918 and 10 November 1918, and finally a belligerent country in the Entente between 10 and 11 November 1918.

At the start of World War I, King Carol I of Romania favored Germany, while the nation's political elite favored the Entente. As such, the crown council took the decision to remain neutral. But after King Carol's death in 1914, his successor King Ferdinand I favored the Entente. For Romania, the highest priority was taking Transylvania from Hungary, with around 2,800,000 Romanians out of around 5,000,000 people. The Allies wanted Romania to join their side in order to cut rail communications between Germany and Turkey, and to cut off Germany's oil supplies. Britain made loans, France sent a military training mission, and Russia promised modern munitions. The Allies promised at least 200,000 soldiers to defend Romania against Bulgaria to the south, and help it invade Austria.

At the outbreak of hostilities, the Austro-Hungarian Empire invoked a casus foederis on Romania and Italy linked to the secret treaty of alliance since 1883. However, both Italy and Romania refused to honor the treaty on the grounds that it was not a case of casus foederis because the attacks on Austria were not "unprovoked", as stipulated in the treaty of alliance. In August 1916, Romania received an ultimatum to decide whether to join the Entente "now or never". Under the pressure of the ultimatum, the Romanian government agreed to enter the war on the side of the Entente, although the situation on the battle fronts was not favorable.

The Romanian campaign was part of the Eastern Front of World War I, with Romania and Russia allied with Britain and France against the Central Powers of Germany, Austria-Hungary, the Ottoman Empire, and Bulgaria. Fighting took place from August 1916 to December 1917 across most of present-day Romania, including Transylvania, which was part of the Austro-Hungarian Empire at the time, as well as in Southern Dobruja, which is currently part of Bulgaria.

The Romanian campaign plan (Hypothesis Z) consisted in attacking Austria-Hungary in Transylvania, while defending Southern Dobruja and Giurgiu from Bulgaria in the south. Despite initial successes in Transylvania, after German divisions started aiding Austria-Hungary and Bulgaria, the Romanian forces (aided by Russia) suffered massive setbacks, and by the end of 1916 out of the territory of the Romanian Old Kingdom only Western Moldavia remained under the control of the Romanian and Russian armies.

After several defensive victories in 1917 at Mărăști, Mărășești, and Oituz, with Russia's withdrawal from the war following the October Revolution, Romania, almost completely surrounded by the Central Powers, was also forced to drop out of the war. It signed the Treaty of Bucharest with the Central Powers in May 1918. The parliament signed the treaty, however King Ferdinand refused to sign it, hoping for an Allied victory on the western front. On 10 November 1918, just one day before the German armistice and after all the other Central Powers had already capitulated, Romania re-entered the war after the successful Allied advances on the Macedonian front.