The Bulgarian population in Pirin Macedonia remained Bulgarian after 1913. The "Macedonian question" became especially prominent after the Balkan wars in 1912–1913, followed from the withdraw of the Ottoman Empire and the subsequent division of the region of Macedonia between Greece, Bulgaria and Serbia. The Slav – speakers in Macedonia tended to be Christian peasants, but the majority of them were under the influence of the Bulgarian Exarchate and its education system, thus considered themselves as Bulgarians. Before the Balkan Wars the regional Macedonian dialects were treated as Bulgarian and the Exarchate school system taught the locals in Bulgarian. Following the Balkan wars the Bulgarian Exarchate activity in most of the region was discontinued. After World War I, the territory of the present-day North Macedonia came under the direct rule of the Kingdom of Yugoslavia and was sometimes termed "Southern Serbia". Together with a portion of today's Serbia, it belonged officially to the newly formed Vardar Banovina. An intense program of Serbianization was implemented during the 1920s and 1930s when Belgrade enforced a Serbian cultural assimilation process on the region. Between the two world wars in Vardar Banovina, the regional Macedonian dialects were declared as Serbian and the Serbian language was introduced in the schools and administration as official language. There was implemented a governmental policy of assassinations and assimilation. The Serbian administration in Vardar Banovina felt insecure and that provoked its brutal reprisals on the local peasant population.