In the early 1900s instability in the Balkans continued, as the collapse of the Ottoman Empire progressed. After an anti-Ottoman rebellion in Macedonia and an Ottoman defeat in the Italo-Turkish War, Bulgaria, Greece, Serbia and Montenegro settled their differences and formed a coalition against the Ottoman Empire, known as the Balkan League. In late September 1912, both the League and the Ottoman Empire mobilised their armies. Montenegro was the first to declare war, on 25 September. The other three states, after issuing an impossible ultimatum to the Sublime Porte on 13 October, declared war on 17 October. Bulgaria was militarily the most powerful of the four states, with a large, well-trained and well-equipped army. The peacetime force of 60,000 men was expanded during the war to 370,000 (more than half of the League's total of 700,000 troops), with almost 600,000 men mobilised in total, out of a population of 4,300,000. The field army counted for 9 infantry divisions, 1 cavalry division and 1,116 artillery units. Bulgarian troops marked a decisive victory at Kirk Kilisse and captured Adrianople after a prolonged siege. A British war correspondent of the era compared the determination of Bulgarian troops to kill their enemy with that of the Japanese and the Gurkhas.