Since it was very clear that neither the Austro-Hungarians nor the Russian were going to give up without a fight, Romania's leaders sought to exploit the opportunity offered by the outbreak of war and liberate the occupied territories. The only question was which ones. With Russia on the side of the Western Allies ( known as the Antante ) and Austro-Hungary on the side of Germany ( the Central Powers ), it didn't seem possible to free all the provinces ( in the end it was, because of the Russian revolution ). Nevertheless, in the eyes of the population, Austro-Hugary was the enemy, since Transilvania was by far the largest and richest of all the provinces, and it was well-known that the Romanians suffered from discrimination and widespread abuse of the Hungarian authorities. So by late 1915, the decision to enter the war on the Antante side had virtually been taken. It was now a matter of when to go to war.

Romania had actually been an ally of Germany since 1888, when king Carol I had signed an alliance treaty with Germany and Austro-Hungary, but this treaty had been kept very secret. Only the king and a few high-ranking officials knew of its existance, since the Romanian public would never have agreed to an alliance with Austro-Hungary. It is of no surprise that king Carol I was favorable to Germany, if one thinks that he was a German prince from the Hohenzollern-Sigmaringen family. In 1914, he pulled out the treaty and tried to persuade the Council of Ministries that Romania should enter the war on the Central Powers's side. Still, the Council refused, for the same reasons as the Italians : Romania had not been warned or consulted by the Gemans as the treaty demanded, so it had no obligation to follow them. For the next two years, the country would stay neutral and negociate, waiting for the right moment.

Slowly, but certainly, Romania approached the Antante, and by the spring of 1916, the terms of the alliance treaty were being discussed. By this stage, the hard-pressed western allies were very eager to relieve some of German pressure on the west front, and requested that Romania enter the war "Now or never". Apart from the political terms, there was a military convention as well. According to it, Romania had to mobilise its full forces "no later than August the 15th 1916" and declare war on Austro-Hungary. The Romanian army was to launch immediately an offensive, whose ultimate goal was to reach Budapest.

On the other side, the Russian army was supposed to act "very strong" on the entire east front, particularly in Bucovina, to cover the mobilization and concentration of the Romanian army. Two Russian infantry divisions and a cavalry division were to enter Dobrogea and assist the Romanian army in defending it against the combined Bulgarian and German troops. The Russian Black Sea fleet was tasked with guarding the Constanta harbour and defending the Romanian seaside from any enemy landings. France and Britain promised that their troops would also launch an offensive on the Greek front ( known as the Salonic front ), to pin down most of the Bulgarian army. Massive deliveries of airplanes, machine guns, heavy artillery pieces gas masks, industrial equipment and ammunitions were also promised.

Unfortunately, the Antante would not keep its end of the bargain. The Russian troops arrived late and there was no Allied offensive in Greece. Following the fall of Serbia, the only way of delivering war materials to Romania was through Russia, which meant that Allied help arrived very late and in smaller quantities than it was supposed to.The French high command was actually more interested in seeing some German units withdrawn from the west front, whilst the Russians considered that Romania shouldn't be defended, except for the eastern province of Moldavia. These attitudes were to have grave consequences for the outcome of the 1916 campaign.

From a military point of view, Romania's situation was not very good in 1916. Her neighbours were : to the north and west Austro-Hungary ; to the southwest the kingdom of Serbia,which had been occupied by the Central Powers ; to the south, Bulgaria ; to the east Russia. Therefore, there were actually two fronts : along the Carpathian mountains, beyond which lay Transilvania and the Austro-Hungarian forces ; along the river Danube, across which stood the Bulgarian army. Between them, these fronts stretched for over 1400 km, making the Romanian front one of the largest.

During 1915 and early 1916, most of the regular army ( about 135000 men ) had been concentrated near the passes through the Carpathians, as requested by the operational planning. There was some attempt to fortify those passes under Romanian control as well, although the works were far less impressive than those of the west front. Usually, a defense position consisted of 2-3 trench lines positioned 100-200 apart from each other and reinforced with barbed wire, earth and log bunkers. The shelters could withstand light and medium artillery fire, but could be destroyed by sustained heavy artillery bombardments. Still, little importance was given to defensive works, as maneuver and attack were the preferred forms of combat. In Dobrogea where the Bulgarian army could be expected to attack, a few cities ( Turtucaia, Silistra and Cernavoda ) had been fortified to some extent to underline their status of "bridgeheads" ( they were situated across the Danube ) , but little else had been done. The forces deployed in the north, were divided into 17 "covering groups", covering the main axes of advance into Transilvania. Their mission was to achieve surprise and capture all the mountain passes very quickly, then cover the great mobilisation, should war be declared.