 Slovenian nationalists such as Anton Korošec also endorsed Yugoslav unification during the First World War, seeing it as a means to free Slovenia from Austro-Hungarian rule.Yugoslavism also had support among Bulgarians, most notably Aleksandar Stamboliyski.However, Bulgarian nationalists resented Serbia's annexation of Vardar Macedonia in 1913, a region they had sought to incorporate into Bulgaria, and the Bulgarian government thus rejected a pan-South Slavic unification led by Serbia, and fought against Serbia on the side of the Central Powers who had promised Bulgaria Vardar Macedonia in exchange for their alliance.