sentences:  For the sake of stopping the Ottoman conquering and possible assault on the capital of Vienna, the large areas of Croatia and Slavonia (even Hungary and Romania) bordering the Ottoman Empire were organized as a Military Frontier which was ruled directly from Vienna military headquarters.The invasion caused migration of Croats, and the area which became deserted was subsequently settled by Serbs, Vlachs, Germans and others.The negative effects of feudalism escalated in 1573 when the peasants in northern Croatia and Slovenia rebelled against their feudal lords due to various injustices.