It was the border area of the Habsburg monarchy, at first just defence strip against the Ottomans and later on it developed into a large Austro-Hungarian war province; in the European history known as a particular political and social phenomenon. Serbian population in the military frontier enjoyed special respect and protection by the Austrian Court, as well as political freedom in comparison to the local landowners and rules. The rights, obligations and property of the Frontiersmen were regulated by special imperial decrees.
German name: Militärgrenze.
The defence line established by King Matthias Corvinus went in the direction Vrbas – Usora – Srebrenik – Šabac – Belgrade. At the back of the Senj Captaincy there were towns Gacko, Otočac, Starigrad and Novigrad at the Zrmanja river mouth.
In the early 19th century, the population of the Military Frontier was 500,000 Serbs and a fewer number of Croats, Romanians, Hungarians and Germans.
In the mid 15th century, after the fall of Bosnia, the Hungarian King Matthias Corvinus organised an defence outpost against the Ottomans and Venice, establishing a separate military area called the Senj Captaincy.
In the late 15th century, the Croats – after a war defeat – retreat to the north, leaving behind the deserted land. The Serbs then settle in the regions of Lika and Krbava.