Bulgaria sustained the heaviest casualties of any of the allies, and on this basis felt entitled to the largest share of the spoils. The Serbs, in particular, did not see things this way and refused to vacate any of the territories they had seized in northern Macedonia (that is, the territory roughly corresponding to the modern Republic of North Macedonia), stating that the Bulgarian 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 south-east. The war was now definitely 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.