When it entered the First World War, Romania was in a geostrategic nightmare: it had to fight on two fronts spanning about 1.500 kilometres. To handle this situation, the Great General Headquarters developed a battle plan called Hypothesis Z.

Romania had been a member of the Triple Alliance ever since 1883. The last time the military convention with the Central Powers was renewed was in December 1912. The agreement provided that in the event of a military conflict between Austria-Hungary and the Russian Empire, the Romanian army had to cross the Prut River and to advance towards Kiev. Following the Balkan Wars and increased tensions with Austria-Hungary, the political and military factors in Bucharest began to increasingly mull over a war against Austria-Hungary. In the summer and autumn of 1914, the Great General Headquarters worked tirelessly on a battle plan against Austria-Hungary. In 1915, when it became certain that Bulgaria would join the Central Powers (September 1915), Romania was in a nightmarish situation: a war on two fronts. To get a handle on this situation, a new military operations plan called Hypothesis Z was elaborated. The objective was clear: “to conquer the territory inhabited by Romanians from the Austro-Hungarian Monarchy”. The development of Hypothesis Z was determined by the extremely difficult strategic position in which Romania found itself, somewhat similar to Germany, having to fight on two fronts. For this reason, many historians have likened Count Alfred von Schlieffen’s plan to Romania’s Hypothesis Z.

The Transylvanian campaign

According to Hypothesis Z, the Romanian army had to commit the bulk of its troops on a north-western direction, over the Carpathian Mountains, and on the southern frontier, on the border with Bulgaria, the rest of the remaining troops had to conduct defensive operations. The final version of Hypothesis Z was finalized at the beginning of August 1916. A few weeks later, on August 27, 1916, Romania joined the Entente and declared war on Austria-Hungary. According to Hypothesis Z, three Romanian armies, the First, Second and North, with a total of almost 370.000 soldiers, representing almost 65% of the total operational forces had to occupy Transylvania according to a strict timetable. In the first phase they had to advance to the Mureș River, which would have shortened the front from 950 to 300 km, while also offering Romanian troops a natural obstacle in the event of a possible counterattack. It also provided adequate possibilities for rail transport. In the second phase, Romanian soldiers had to continue advancing to the north and west, respectively to Cluj, Deva and the Apuseni Mountains. In the third and final phase, the Romanian troops had to advance to Oradea and enter the Hungarian Plain and head towards Debrecen. The Romanian General Staff had correctly estimated that the troops had to face no more than 100.000 Austro-Hungarian soldiers.

The southern border of Romania was defended by the Third Army, composed of about 140.000 soldiers, or 25% of the available troops. Its mission was to provide the necessary leeway for the units advancing into Transylvania, by neutralising possible attacks by Bulgarian troops. The big problem of the Third Army was the very large distance it had to cover, and as this was not a big enough problem, the operations of the Third Army had to be carried out in two phases. The first phase was purely defensive. In the second, after the Russian expeditionary force occupied its defensive positions, the troops of the Third Army had to go on the offensive and destroy the enemy forces in north-eastern Bulgaria and occupy the Ruse-Varna area.

The problems of Hypothesis Z

Hypothesis Z, however, had some weaknesses that would prove to be the undoing for the Romanian army. First of all, the pace set for the advance to the Mures River was very slow, 25 days negated any rapid exploitation of the weaknesses of the Austro-Hungarian troops in Transylvania. It should have been expected, as it in fact happened, that the Central Powers would quickly react and send reinforcements to Transylvania. Hypothesis Z did not take into account the possible reinforcement of the Austro-Hungarian troops from Transylvania. It was unthinkable that Germany would have allowed Romanian troops to enter central Hungary without sending troops from other fronts or reserves. Yet another problem was the cooperation with a reluctant Russian ally that wasn’t very determined to support the Romanians in this endeavour.

On the southern front, Hypothesis Z did not take into account other aspects. It was assumed that the vast majority of Bulgarian-German forces would have been tied down on the Thessaloniki Front, which did not happen.


Glenn E. Torrey, România în Primul Război Mondial [Romania in the First World War], Meteor Publishing House, Bucharest, 2014.

I.G. Duca, Memorii [Memoirs], vol. I, Expres Publishing House, Bucharest, 1992.

The Count of Saint-Aulaire, Însemnările unui diplomat de altădată: În România: 1916-1920 [The testimonies of a former diplomat: In Romania: 1916-1920], Humanitas Publishing House, Bucharest, 2016.

Constantin Argetoianu, Memorii [Memoirs], Humanitas, Bucharest, 1992.

Florin Constantiniu, O istorie sinceră a poporului român [A sincere history of the Romanian people], Encyclopaedic Universe Publishing House, Bucharest, 2008.

Translated by Laurențiu Dumitru Dologa