 The extent of the Ottoman conquest still marks the southern and eastern boundaries of Croatia proper as a geographical region.In effect, Croatia proper loosely corresponds to what was termed the relics of the relics of the formerly great and glorious Kingdom of Croatia () and subsequent Kingdom of Croatia within the Habsburg Empire.The Croatian Military Frontier was gradually established in the second half of the 16th century, removing further territory from the Kingdom of Croatia and placing the military zone under direct imperial rule.