The Voivodeship of Carantania primarily consists of the Styria Krajina, the Carinthia Krajina which consists of a large part of Carinthia and the Burgenland Krajina which consists of most of Burgenland.
Although technically a recent creation, the Carantanian Voivodeship is considered to be the successor state of Samo's Empire, which is the earliest known Slavic state. Another one of its predecessor states is the March of Carinthia and the March of Styria, both of which later became duchies.
By the 15th century, the Carantanian region had been controlled by the Archduchy of Austria and its House of Habsburg. After the two wars against Austria had been finished, Croatia became the ruler of the initial Carantanian nation. Although initially merely a mix of Germans, Slavs and Italians, it was soon molded with the coastal areas becoming Croatian while the Carantanian heartland became more Carantanian.
After a period of direct rule by the Croat nation, the Archvoivodeship's government passed a decree that created the Carantanian nation as the Carantanian Voivodeship.