Four minor regions (historiographically referred to by Bulgarians as the Western Outlands) had been part of Bulgaria from its inception as a principality in 1878, except for the region around Strumitsa, which became part of Bulgaria in 1912. Bulgaria was internationally recognised as an independent country in 1908 and controlled these territories until 1919 when they were ceded to the Kingdom of the Serbs, Croats and Slovenes under the Treaty of Neuilly. The cession of the region was partly a compensation for the occupation of the southern and eastern part of Serbia by Bulgarian troops between 1915 and 1918, and was partly motivated by strategic reasons. The old political boundary between Bulgaria and Serbia followed a chain of high mountain ridges, whereas the new one gave significant military and strategic advantages to the Serbs: it dangerously exposed the Bulgarian capital of Sofia and significantly reduced the military threat to eastern Serbia in case of a Bulgarian invasion (see also Balkan Wars and World War I).