As they had proven valuable during the Balkan Wars, the Serbian army used Chetniks in World War I in the same way, and while useful they suffered heavy losses. At the end of the Serbian campaign of 1914–1915, they withdrew with the army in the Great Retreat to Corfu and later fought on the Macedonian front. Montenegrin Chetniks also fought against the Austro-Hungarian occupation of that country. In late 1916, new Chetnik companies were being organised to fight in Bulgarian-occupied southeastern Serbia. Concerned about reprisals against a large-scale uprising, the Serbian army sent the veteran Chetnik leader Kosta Pećanac to prevent the outbreak. However, the Bulgarians started conscripting Serbs, and hundreds of men joined the Chetnik detachments. This resulted in the 1917 Toplica Uprising under the leadership of Kosta Vojinović, which Pećanac eventually joined. Successful at first, the uprising was eventually put down by the Bulgarians and Austro-Hungarians, and bloody reprisals against the civilian population followed. Pećanac then used Chetniks for sabotage and raids against the Bulgarian occupation troops, then infiltrated the Austro-Hungarian occupied zone. Just prior to the end of the war, the Chetnik detachments were dissolved, with some sent home and others absorbed by the rest of the army. The Kingdom of Serbs, Croats and Slovenes was created with the merger of Serbia, Montenegro and the South Slav-inhabited areas of Austria-Hungary on 1 December 1918, in the immediate aftermath of the war.