army had failed to accomplish its pre-war goals at Adrianople (i.e., failing to capture it without Serbian help) and that the pre-war agreements on the division of Macedonia had to be revised. Some circles in Bulgaria inclined toward going to war with Serbia and Greece on this issue. In June 1913 Serbia and Greece formed a new alliance, against Bulgaria. The Serbian Prime Minister, Nikola Pasic, told Greece it could have Thrace if Greece helped Serbia keep Bulgaria out of the Serbian part of Macedonia, and the Greek Prime Minister Eleftherios Venizelos agreed. Seeing this as a violation of the pre-war agreements, and discreetly encouraged by Germany and Austria-Hungary, Tsar Ferdinand declared war on Serbia and Greece and the Bulgarian army attacked on June 29. The Serbian and the Greek forces were initially on the retreat on the western border, but they soon took the upper hand and forced Bulgaria into retreat. The fighting was very harsh, with many casualties, especially during the key Battle of Bregalnica. Soon Romania entered the war and attacked Bulgaria from the north. The Ottoman Empire also attacked from the southeast. The war was now lost for Bulgaria, which had to abandon most of her claims of Macedonia to Serbia and Greece, while the revived Ottomans retook Adrianople. Romania took possession of southern Dobruja. World War I In the aftermath of the Balkan Wars Bulgarian opinion turned against Russia and the western powers, which the Bulgarians felt had done nothing to help them. Bulgaria, Romania, and Greece were content to sit on the fence and observe the fortunes of war before deciding whether to declare their sympathies. The government of Vasil Radoslavov aligned Bulgaria with Germany and Austria-Hungary, even though this meant also becoming an ally of the Ottomans, Bulgaria's traditional enemy. But Bulgaria now had no claims against the Ottomans, whereas Serbia, Greece, and Romania (allies of the UK and France) were all in possession of lands perceived in Bulgaria as Bulgarian. Bulgaria, recuperating from the Balkan Wars, sat out the first year of World War I, but when Germany promised to restore the boundaries of the Treaty of San Stefano, Bulgaria, which had the largest army in the Balkans, declared war on Serbia in October 1915. The UK, France, Italy, and Russia then declared war on Bulgaria. Bulgaria, in alliance with Germany, Austria-Hungary, and the Ottomans, won military victories against Serbia and Romania,