After remaining neutral for two years, Rumania—miscalculating the apparent success of Russia's Brusilov Offensive—chose to enter the war on the side of the Entente on 27 August 1916. The government's prime motive, like Italy's in 1915, was to obtain more territory. King Ferdinand and Premier Ion Bratianu, however, had grossly overestimated the fighting power of their army and the weakness of the Central Powers.
|Rumanian Infantry Form a Skirmish Line|
Following an initial advance across the Transylvanian Alps into Hungary, Rumania was invaded from two directions. From Bulgaria in the south, a combined force of Germans, Turks, and Bulgarians under the command of Field Marshal August von Mackensen attacked between the Danube and the Black Sea. Rumania moved troops from the advancing forces in Transylvania to oppose the counter-invasion which threatened all of their Black Sea ports as well as Bucharest, the capital. Then in late September, General Falkenhayn, recently demoted as chief of staff, arrived to take command of the German Ninth Army in Transylvania to the north. He quickly attacked, capturing Hermanstadt and driving two Rumanian divisions back into the mountains.
In quick order the two German commanders and a third Austro-Hungarian force relentlessly crushed the Rumanian opposition. By 5 December Bucharest had fallen, Rumania's oil fields had been set ablaze, and three-fourths of Rumania was occupied. The arrival of Russian forces staved off total disaster. A defensible line was formed on the Sereth River in the northeast, allowing Rumania to retain a major portion of Moldavia.
|Germany Cavalry Pursuing Rumanian Troops|
There was little action in the next year, but in December 1917, the exhausted Rumanian government had to ask the Central Powers for terms. They had lost a war and suffered over 400,000 casualties for their territorial ambitions. Things would change dramatically for Rumania at the Paris Peace Conference, where their delegation cleverly negotiated an outcome that saw them gain significant additional territory, as well as shipments of arms and military support. They not only recovered territory that was lost to Bulgaria but they also gained additional territory by acquiring Transylvania.