Hello there,

The lands you mentioned were sparsely populated because of almost four hundred years of conflict between the Monarchy and the Ottoman Empire and yielded little, if any levied agrarian/mineral resources for the Habsburg Monarchy after they came under their control. The ongoing conflict between the two states prevented any meaningful governance by the Habsburg Monarchy and forced them to place the border provinces under the control of their central military administration board, the Hofkriegsrat.

This border served as a buffer between the kingdoms of the Monarchy and was known as the ‘Military border’. Most of northern Bosnia, Croatia and northern Serbia sat within the Hofkriegsrat’s jurisdiction, which instead of being taxed was instead levied for military service. Men were expected to report for duty in the Grenzer Regiments of the Imperial army, whose roles transformed from border raiders to light infantry to a legitimate part of the army.

During the eighteenth century, after the threat of the Ottoman Empire had rescinded, Joseph II initiated a significant resettlement policy, which offered to facilitate the move of peoples from the Reich and Bohemia to these regions. The first objective was to improve the land yield and the percentage of Christian ‘German’ subjects found in these new territories. The second, was to increase the subjects available for recruitment into the border regiments. These state sponsored migrations, which saw a significant change to the social fabric of the region, is why we can now find some areas in these nations with a history of Bohemian, northern Hungarian and Moravian settlement.

Check Gunther Rothenberg's work on the Military border, starting with The Austrian military border in Croatia, 1522-1747 and The Austrian Military Border in Croatia, 1740–1881; a Study of an Imperial Institution.