The Vrbas Banovina or Vrbas Banate (Serbian, Bosnian, and Croatian: Врбаска бановина/Vrbaska banovina) was a province (banovina) of the Kingdom of Yugoslavia between 1929 and 1941. It was named after the Vrbas River and consisted mostly of territory in western Bosnia (part of historical and present-day Bosnia and Herzegovina) with its capital at Banja Luka. A Dvor district of present-day Croatia was also part of the Vrbas Banovina.
Read more about Vrbas Banovina: Borders, Population, History