On August 27, 1916, Rumania declared war on Austria-Hungary. Like Italy, Rumania had been a neutral state with treaty obligations that theoretically bound it to the Central Powers, but opportunism inspired an alliance with the Entente instead. Also like Italy, Rumania was poorly prepared for war. The consequences for Rumania were far more devastating than for Italy, because the prospects for direct aid from the Entente were limited, while the Central Powers were well-placed to mount a unified and highly-orchestrated counterattack.
Rumania in 1916 was a country with abundant natural resources, particularly in food and fuel, but with a poor military characterized by obsolete equipment and inadequate training. The value of the natural resources was enough to inspire competition for Rumania’s support. The dynastic relationship between the Rumanian Crown and the German Kaiser is often cited as a reason to expect the Rumanians to join the Central Powers, but like Italy, Rumania would have had little prospect for territorial aggrandizement as an ally of Germany, Austria-Hungary, Bulgaria and Turkey. As an ally of the Entente, Rumania had the possibility of gaining Transylvania, Bukovina and the Banat, if the Russians did not get them first.
This was the consideration that governed both Rumania’s decision and its timing. Rumania had already secured the support of Britain for the seizure of Transylvania, but Russia was not persuaded. Russian successes in the Brusilov Offensive in 1916 forced the issue: if the Rumanians waited any longer, they risked seeing Russian armies marching into Transylvania instead of Rumanian ones. They made a final diplomatic effort to secure support in the Entente for their claims on Transylvania, Bukovina and the Banat. Winning grudging support, they promptly declared war on Austria-Hungary (avoiding any mention of Germany in the process), sending the 1st, 2nd and 4th Armies into Transylvania on the same day.
Only Erich von Falkenhayn, Chief of the German General Staff, was surprised, and this was the final piece of bad news in a series of setbacks that ended his tenure in this post. The Germans had already made contingency plans for a Rumanian belligerency, and as Generals Hindenburg and Ludendorff took up the leadership of the General Staff vacated by Falkenhayn, it fell to them to activate the plans as efficiently as possible. The result was a campaign that unfolded with the decisiveness that commanders on both sides so dearly desired.
Rumania in 1916 was shaped like a crescent, with its center pointing at the Black Sea. The province of Moldavia extended north between Hungary and Russia, while Wallachia extended west between Hungary and Bulgaria. The German plan called for a pincer attack against the center through Transylvania and Wallachia in the northwest and the coastal region of the Dobruja from the south. The sweep through Transylvania was to be carried out by a joint German-Austrian army, the Ninth, freshly under the command of Falkenhayn, and the Austrian 1st Army. The southern sweep was effected by a newly-raised formation, the Danube Army, under the command of the very capable German General August von Mackensen. The Danube Army combined Bulgarian forces with Mackensen’s German troops and a limited amount of Turkish support. In this way, all four of the Central Powers participated in this joint mission.
Rumanian plans were far more muddled. The Rumanians expected little resistance from Austria-Hungary as they marched through Transylvania, and indeed, they managed to push some 50 miles into enemy territory. While they had hoped to fight Austria-Hungary alone, and forestall intervention by the other Central Powers, they never expected this to work, and they expected to face German and Bulgarian troops eventually. Against the former, the Rumanians expected Russian help; against the latter, they anticipated support from the western Allies through Salonika. Neither was fully realized. In the north, the Russians held a line at the eastern edge of the Carpathians, shielding much of Moldavia, but offered no other meaningful support for the Rumanian adventure until the retreat to Moldavia in December; in the south, Entente efforts at Salonika came to nothing, and the only aid that Rumania received came from a Russian army sent south to reinforce the Dobruja.
The attack of the Central Powers came swiftly. The original Rumanian invasion had been on August 27; on the 29th, Falkenhayn was reassigned, and replaced by Hindenburg. The attack of the Danube Army against the Dobruja began on September 1, and made steady progress until the 23rd, when the combined Rumanian and Russian force halted the advance some miles from the cities of Constanza and Cernavoda. Large but outdated fortifications at Turtukai and Silistria fell quickly when tested by the heavy German artillery. The northern contingent required some more time to begin its part in the invasion, but on September 18, Falkenhayn was ready to attack the Rumanians on Hungarian soil. These operations proceeded quickly, with the chief challenges being posed by autumn rains and the occasional tendency of troops to outrun their own supply lines. By October 10, Ninth Army had cleared the Rumanians from its sector of Hungary, but the Rumanians were able to hold several passes of the Transylvanian Alps until November.
The act of securing these passes before winter set in was crucial. Ninth Army was able to cross the mountains and seize Campolung by October 14, but further gains in the north were forestalled for the rest of the month. The Danube Army broke its deadlock on October 20, resuming its advance up the coast. Constanza and Cernavoda fell on October 25, and from these cities, the Danube Army marched halfway to the Russian border before it was again stopped.
Plans for November called for different objectives. Ninth Army forced its way through the western alpine passes and marched deep into Wallachia, capturing Craiova by November 21. Two days later, reserve units of the Danube Army emerged from Sistova to force their way across the river. Approaching the capital city, Bucharest, these units prompted a Rumanian counterattack on December 1. The effort was coordinated by a French observer, Henri Berthelot, but he had little in the way of material, and even if the attack had not failed, it would have had little effect: even while it proceeded, Ninth Army crossed the River Arges and approached Bucharest from the north.
The Rumanian government had already acknowledged that Bucharest was indefensible, and left the capital for Iasi, at the eastern end of Moldavia. It was met, gradually, by stragglers from the army that were able to escape from the Central Powers; ultimately, however, it was the Russians that defended Moldavia.
The Germans captured Bucharest on December 6, and this marked the end of organized conflict in Rumania. British commandos made a token gesture of defiance by destroying fuel reserves at Ploesti, but most of Rumania would remain in the hands of the Central Powers for the rest of the war. Technically, Rumania continued the war for a full year after the fall of Bucharest; only after the Bolsheviks seized power in Russia did the Rumanians sue for peace, with the agreement being reached on December 7, 1917.
The Rumanian declaration of war had been ill-considered in principle and ill-timed in execution. The response of the Central Powers, on the other hand, serves as a model for what military forces during World War I could accomplish, if used effectively and realistically. In part, however, it worked because of factors that could not be replicated on any other front. It was a rare example of a decisive military campaign at the height of the period characterized by battles of attrition.
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