The rebellion included the areas of Toplica, Jablanica, Jastrebac, eastern and central parts of Kopaonik. The rebels liberated Kuršumlija , Lebane , Prokuplje  and Blace . Having broke out in the Toplica region, the rebellion expanded into territories on the right bank of the West Morava , and in the West Morava valley, included the Sokobanja and Svrljig areas. On March 12, the Bulgarian counter-attack started under the command of Alexander Protogerov involving IMRO forces led by Tane Nikolov. Bulgarian and Austro-Hungarian authorities worked together. IMRO commander and Bulgarian officer Todor Aleksandrov orchestrated the most violent actions committed by Bulgarian paramilitary. After several days of fighting, the Bulgarians entered Prokuplje on 14 March and the Austro-Hungarians entered Kuršumlija on 16 March. As of 25 March, the order there was fully restored. In the battles, several thousand people were killed, including civilians. In April 1917, Pećanac with his guerrillas, attacked a railway station. On May 15, Pećanac entered the old Bulgarian border and invaded Bosilegrad, which was burned. Then his band withdrew to Kosovo, controlled then by the Austro-Hungarians. The Allies opened a new front at Salonika in June but the Serbian Army was unable to break through the Bulgarian lines. After reemerging again for a short time, in September - October 1917 Pećanac again disappeared. In October 1917 the Austro-Hungarian command created entirely Albanian paramilitary detachments to capture the rest of the Serbian rebels into the mountains and in December 1917, Kosta Vojinović was killed.

Based on the above article, answer a question. Who led Bulgaria at the beginning of the conflict?
Alexander Protogerov