Question: What southern part of the Kingdom of Slavonia straddled the borderland of the Habsburg Monarchy?

Related documents: [0]  [DOC] The Military Frontier was a province straddling the southern borderland of the Habsburg Monarchy and later the Austrian and Austro-Hungarian Empire. It acted as the "cordon sanitaire" against incursions from the Ottoman Empire. [END] 
[1]  [DOC] The Kingdom of Slavonia (Croatian: "Kraljevina Slavonija" ; German: "Königreich Slawonien" ; Latin: "Regnum Sclavoniae" ; Hungarian: "Szlavón Királyság" ) was a province of the Habsburg Monarchy and the Austrian Empire that existed from 1699 to 1868. The province included northern parts of present-day regions of Slavonia (today in Croatia) and Syrmia (today in Serbia and Croatia). The southern parts of these regions were part of the Slavonian Military Frontier, which was a section of the Military Frontier. [END]  
Answer: The Military Frontier
The Military Frontier