to win new allies, especially in the Balkans. Bulgaria's main aim was to regain Macedonia but Serbia was unwilling to make any compromises which gave the German diplomacy a great advantage. The general military situation also favored the Central Powers—the Germans were holding firm on the Western Front and on the Eastern Front their Gorlice–Tarnów Offensive ended in major defeat for the Russians. Under these circumstances on 6 September (24 August) 1915 at the German military headquarters in Pleß Bulgaria and Germany signed a treaty of alliance. A military convention, which included Austria-Hungary as a third party and laid the plan for the conquest of Serbia, was also concluded. In accordance with the convention Bulgaria began mobilizing and concentrating its forces its western border. For the campaign the Bulgarian high command planned to attack Serbia with two armies. The First Army under the command of Lieutenant General Kliment Boyadzhiev was deployed between the Danube and Tran. As stipulated by the military convention it was part of Army Group Mackensen together with the German Eleventh Army and the Austro-Hungarian Third Army. On 1 October(14 October) 1915 the army had the following organization: The Serbians were informed about the Bulgarian war preparations by their military attaché in Sofia and the units covering the border between the two countries. Once Bulgaria declared mobilization the Serbian High Command planned a preemptive strike against the Bulgarian forces who were still concentrating and organizing on the border. For that purpose it deployed the entire Second Army, the Timok Army, the Kraina detachment and the Vlasinski detachment against the sector of the Bulgarian First Army. These were sizable forces of around 100 battalions with 90,000 rifleman, 248 cannons and 94 machine guns. In addition the Serbians also had a defensive alliance with Greece and hoped the Greek Army would also intervene. The Serbs have also asked the Entente for assistance in the form of a 150,000 strong army. Although the Entente couldn't provide the troops the Serbian army was prepared to attack Bulgaria. However, the Serb Prime Minister Pašić did not dare to attack Bulgaria over explicit opposition of all the Allied Powers (Russia, France and Great Britain). On 1 October(14 October) 1915 Bulgaria declared war on Serbia and the First Army was ordered to begin its Morava Offensive. Its primary objectives were to push the Serbian forces out of the Timok and Morava valleys, to link