The Kingdom of Serbs, Croats and Slovenes was formed in 1918 and was initially divided into counties and districts (this division was inherited from previous state administrations).

In 1922, the country was divided into 33 new administrative units known as oblasts (Serbo-Croatian: oblasti / области).

Before 1922, the territory of the Vrbas Oblast was primarily part of the Banja Luka District.

The Vrbas Oblast included eastern Bosanska Krajina and western Semberija.

According to the 1921 census, the Vrbas Oblast was linguistically dominated by speakers of Serbo-Croatian.