site.btaNovember 6, 1920: Serbia Occupies Western Outlands as per Treaty of Neuilly

After the end of the First World War (1914-1918), the victorious Entente coalition imposed on the Central Powers a system of treaties known as the "Versailles Treaty System". Five peace treaties were drafted and concluded. The one concerning Bulgaria was concluded at Neuilly on November 27, 1919. According to the Treaty of Neuilly, the Western outlands with an area of 1,555 sq. km. and a population of 64,509 people, of whom 54,750 were Bulgarians, 8,637 - Vlachs, 549 - others and only 127 - Serbs, were cut off from Bulgaria. The claims of the Kingdom of Serbs, Croats and Slovenes (since 1929 the Kingdom of Yugoslavia) were for the towns of Vidin, Kula, Belogradchik, Breznik, Tran, Radomir, Kyustendil, Petrich, Tsaribrod (now Dimitrovgrad) and Bosilegrad with their adjacent lands. The Serbian state also claimed the territory around the town of Strumica.

An Inter-Allied Commission was set up to define the exact post-war border. Not waiting for the end of the commission's meetings, on November 6, 1920, Serbian troops occupied the territories around the Timok River, part of the Tran region and the surroundings of Tsaribrod and Bosilegrad. One Bulgarian high school, six secondary schools and 45 churches were closed. A third of the Bulgarian population in the occupied territories was forced to take refuge in the free parts of Bulgaria. The same day, the Bulgarian National Assembly adjourned in protest and declared three days of national mourning. The symbol of this occupation became the black headscarf. Bulgarian women in the occupied lands put on black headscarves as a sign of national mourning, and the border thus drawn was called by the local Bulgarians the "Black Border".

During the Interwar period, local Bulgarians and refugees organized in legal and revolutionary movements aiming at the return of the Western Outlands to Bulgaria. Parallel to the Scientific Institute of the Western Outlands, the Supreme Committee of the Western Outlands, the newspapers Zapadno Eho (Western Echo) and Zapadni Pokraynini (Western Outlands), the Internal Revolutionary Organization of the Western Outlands "Vartop" was created in 1924. It engaged in terror attacks and guerilla warfare against the Serbian authorities. Vartop was active in both Sofia and the occupied lands up until 1934, when it was disbanded by the Bulgarian military.