 The outbreak of the First World War allowed Bulgaria to occupy eastern Macedonia and Vardar Macedonia, helping Austria-Hungary defeat the Serbs by the end of 1915, and leading to the opening of the Macedonian front against the Greek part of Macedonia.Bulgaria would maintain control over the area until their capitulation in September 1918, at which point the borders reverted (with small adjustments) to the situation of 1913, and the present-day Republic of North Macedonia became part of the Kingdom of Serbs, Croats and Slovenes.This period saw the rise of ideals of a separate Macedonian state in Greece.