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.

The military convention they signed with the Allies stipulated that France and Britain should start an offensive against Bulgaria and the Ottoman Empire no later than August 1916, that Russia would send troops into Dobruja, and that the Romanian army would not be subordinated to Russian command.

The German high command was seriously worried about the prospect of Romania entering the war, Paul von Hindenburg writing: It is certain that so relatively small a state as Rumania had never before been given a role so important, and, indeed, so decisive for the history of the world at so favorable a moment.

[39][40][a] Many fought in the battles of Mărăști, Mărășești and Oituz, where with Russian support the Romanian army managed to defeat an offensive by the Central Powers and even take back some territory.

Romanian troops fought on all European fronts of the Dual Monarchy, some of them being distinguished, such as Feldmarschall-leutnant (Lieutenant field marshal) Ioan Boeriu, Oberst (Colonel) Dănilă Papp, Hauptmann (Căpitan) Gheorghe Flondor and Leutnant (Locotenent) Emil Rebreanu.

Other notable Romanians who fought in the Austro-Hungarian Army included Oberleutnant (Locotenent-Major) and Imperial Adviser Constantin Isopescu-Grecul, as well as Octavian Codru Tăslăuanu, who also wrote valuable memoirs about his war experience.

In our moral energy and our valour lie the means of giving him back his birthright of a great and free Rumania from the Tisza to the Black Sea, and to prosper in peace in accordance with our customs and our hopes and dreams.

Animated by the holy duty imposed upon us, and determined to bear manfully all the sacrifices inseparable from an arduous war, we will march into battle with the irresistible élan of a people firmly confident in its destiny.

The Entente incorrectly assumed that Germany would be unable to respond to the invasion, as the Battle of the Somme and the Brusilov Offensive were at their height around this time and tied down significant German forces.

A separate Romanian offensive, carried out by the 1st Infantry Division, was much more limited in its aims and it succeeded: capturing the west bank of the Cerna River within the Banat region.

Mackensen's success was favoured by the failure of the Allies to fulfill the obligation they had assumed through the military convention, by virtue of which they had to mount an offensive on the Macedonian front and the conditions in which the Russians deployed insufficient troops on the battlefront in the south-east of Romania.

[65] The Central Powers succeeded in taking the strategic initiative in Transylvania by concentrating significant military forces rapidly brought in from the other theatres of operations in Europe and exploiting a quick shift of Romanian units to the battlefront in Dobruja.

[61] In October 1916, the Romanian army mounted a wide-scale operation, the main target of which was the defense of the mountain passes in the Southern and Eastern Carpathians against the ever-stronger pressure of the German and Austro-Hungarian forces.

[66] Back on the coast, Field Marshal Mackensen and Bulgarian General Stefan Toshev launched a new offensive on 19 October, after a month of careful preparations, and achieved a decisive victory in the Second Battle of Cobadin.

On 7 November, Romanian anti-aircraft defenses at Sulina (including the old protected cruiser NMS Elisabeta) shot down into the sea one of the seaplanes, killing the commander of the German squadron.

[69][70] This was probably caused by an encounter with the Romanian torpedo boat NMS Smeul, whose captain surprised a German submarine near Sulina in November 1916, the latter reportedly never returning to her base at Varna.

The plan envisaged the checking of the advance of the German Ninth Army from the north and north-west, as well as the encirclement and annihilation of the German-Bulgarian-Turkish units deployed south-east of Bucharest.

[73] Faced with the overwhelming superiority of the invading forces, the Romanian army, its ranks thinned from the previous actions, inferior in equipment and lacking Russian support, failed to check the enemy advance.

[74] The Romanian Second Army made a fighting retreat to the Siret river, which had originally been fortified against the Russians and was facing the wrong direction, but nevertheless would end up proving invaluable, protected as it was by the impassable Danube Delta to the southeast and a flank in the Carpathians in the northwest.

Romania entered the war at a time of strong crisis for the Entente, drawing upon itself numerous enemy forces, fighting on a very long battlefront and having to change its initial campaign plan permanently.

But in spite of the human, material and military efforts made by the Central Powers throughout this period, they failed to achieve their fundamental political and strategic goal to defeat Romania and knock it out of the war.

After the Romanian troops had managed to bring the enemy to a halt at Moldavia's Gates, on the Eastern Carpathians, the Siret River and the Danube Delta alignment in cooperation with Russian military forces, Romania embarked on the reconstruction and strengthening of its combat capability during the first half of 1917 through multiple national efforts under highly complex international circumstances.

Agriculture received special attention to help meet basic nutritional needs and ensure a minimal living standard to the population in the free part of the country, and also to assist the refugees who had left their houses in front of the enemy invasion, the Romanian army and the Russian troops (who numbered about one million by early 1917).

The political life in unoccupied territory adopted a fundamental goal to achieve national consensus to find the means to conclude a successful liberation war.

Within this framework, debates on some laws envisaging structural transformations (primarily the agrarian reform to re-allocate land to peasants and the introduction of universal suffrage) responded to popular demands of the citizenry and contributed to the morale of the soldiers in the front lines.

[82] Considerable progress was achieved with the technical-material equipment of the army by means of its provisioning with armament, ammunition and other combat resources from inside the country, but even more importantly from abroad.

[84] On 16 April, Easter Monday, the Romanian torpedo boat NMS Smeul capsized in rough seas off the mouth of the Danube with the loss of 18 of her crew, including 3 French naval officers present on board.

[86][87] Aware of the complex strategic situation, the Romanian Command lent its military policy a clear, realistic orientation of committing the entire population to battle, trying to act efficiently in keeping with the national goals and in harmony with the large-scale operations worked out at the coalition level.

The three great battles, decisive for the Romanian nation's destiny, delivered at Mărăști, Mărășești and Oituz, represented a turning point in the war on the Eastern front.

When they occupied productive areas, such as southern Romania,[98] they seized food stocks and other supplies for their own purposes and blocked any shipments intended for civilians back in the Austro-Hungarian Empire.