promised at least 200,000 soldiers to defend Romania against Bulgaria to the south, and help it invade Austria-Hungary. On 4 August 1916, Romania and the Entente signed the Political Treaty and Military Convention, which established the parameters of Romania's participation in the war. The Allies promised to Romania the Austro-Hungarian regions of Bukovina, Transylvania up to Tisza river and all of Banat. Joining the Entente had large popular support. The Romanian campaign plan (Hypothesis Z) consisted in attacking Austria-Hungary in Transylvania, while defending Southern Dobruja and Giurgiu from Bulgaria in the south. 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. Never before had two great Powers like Germany and Austria found themselves so much at the mercy of the military resources of a country which had scarcely one twentieth of the population of the two great states. Judging by the military situation, it was to be expected that Rumania had only to advance where she wished to decide the world war in favor of those Powers which had been hurling themselves at us in vain for years. Thus everything seemed to depend on whether Rumania was ready to make any sort of use of her momentary advantage. On 27 August 1916, the Romanian Army launched an attack against Austria-Hungary, with limited Russian support. The Romanian offensive was initially successful and Romania managed to occupy 1/3rd of Transylvania, but when the German army arrived in Transylvania the Romanians began to be pushed back. While on the southern front, a combined German-Bulgarian-Turkish offensive gradually occupied all of Dobruja and captured Giurgiu. The bulk of the Romanian army managed to escape encirclement from Giurgiu and retreated to Bucharest. As a result of the Battle of Bucharest, the Central Powers occupied Bucharest on 6 December 1916. In the summer of 1917, one of the largest concentrations of forces in World War I was present in Romania: 9 armies, 80 infantry divisions and 19 cavalry divisions, totaling 974 battalions, 550 squadrons and 923 artillery batteries. 800.000 combatants and 1.000.000 reservists were present. In 1917, a new Central Powers offensive began, leading to the battles of Mărăști, Mărășești, and Oituz,