The change of leadership was far from a solution to the war with the Ottomans, in fact, the Ottoman Empire gradually expanded in the 16th century to include most of Slavonia, western Bosnia and Lika.
Croatian territory under Habsburg rule was 25 years later reduced to about 20,000 km².
In 1558, the parliaments of Croatia and Slavonia were united after many centuries into one.
The centre of the Croatian state moved northward from coastal Dalmatia, as these lands were conquered by the Ottomans.
The town of Zagreb gained importance, as did nearby Varaždin.

Taking advantage of the growing conflict between King Sigismund II of Poland and Emperor Maximilian II, Suleiman the Magnificent started his sixth raid of Hungary in 1565 with 100,000 troops.
They successfully progressed northwards until 1566 when they took a small detour to capture the outpost of Siget (Szigetvár) which they failed to capture ten years previously.
The small fort was defended by Count Nikola IV Zrinski and 2,300–3,000 men.
They were able to hold their ground for a month, and decimated the Ottoman army before being wiped out themselves.
This siege, now known as the Battle of Szigetvár, bought enough time to allow Austrian troops to regroup before the Ottomans could reach Vienna.

By orders of the king in 1553 and 1578, large areas of Croatia and Slavonia adjacent to the Ottoman Empire were carved out into the Military Frontier (Vojna krajina or Vojna granica) and ruled directly from Vienna's military headquarters.
Due to the dangerous proximity to the Ottoman armies, the area became rather deserted, so Austria encouraged the settlement of Serbs, Germans, Hungarians, Czechs, Slovaks and Rusyns/Ukrainians and other Slavs in the Military Frontier, creating an ethnic patchwork.

The negative effects of feudalism escalated in 1573 when the peasants in northern Croatia and Slovenia rebelled against their feudal lords over various injustices such as unreasonable taxation or abuse of women in the Croatian and Slovenian peasant revolt.
Ambroz Matija Gubec and other leaders of the mutiny raised peasants to arms in over sixty fiefs throughout the country in January 1573, but their uprising was crushed by early February.
Matija Gubec and thousands of others were publicly executed shortly thereafter, in a rather brutal manner in order to set an example for others.

After the Bihać fort finally fell to the army of the Bosnian vizier Hasan Pasha Predojević in 1592, only small parts of Croatia remained unconquered.
The remaining 16,800 km² where around 400,000 inhabitants lived were referred to as the "remnants of remnants of the once great and renowned Kingdom of Croatia" (Latin: reliquiae reliquiarum olim magni et inclyti regni Croatiae).
The change of leadership was far from a solution to the war with the Ottomans, in fact, the Ottoman Empire gradually expanded in the 16th century to include most of Slavonia, western Bosnia and Lika. Croatian territory under Habsburg rule was 25 years later reduced to about 20,000 km². In 1558, the parliaments of Croatia and Slavonia were united after many centuries into one. The centre of the Croatian state moved northward from coastal Dalmatia, as these lands were conquered by the Ottomans. The town of Zagreb gained importance, as did nearby Varaždin.
Taking advantage of the growing conflict between King Sigismund II of Poland and Emperor Maximilian II, Suleiman the Magnificent started his sixth raid of Hungary in 1565 with 100,000 troops. They successfully progressed northwards until 1566 when they took a small detour to capture the outpost of Siget (Szigetvár) which they failed to capture ten years previously. The small fort was defended by Count Nikola IV Zrinski and 2,300–3,000 men. They were able to hold their ground for a month, and decimated the Ottoman army before being wiped out themselves. This siege, now known as the Battle of Szigetvár, bought enough time to allow Austrian troops to regroup before the Ottomans could reach Vienna.
By orders of the king in 1553 and 1578, large areas of Croatia and Slavonia adjacent to the Ottoman Empire were carved out into the Military Frontier (Vojna krajina or Vojna granica) and ruled directly from Vienna's military headquarters. Due to the dangerous proximity to the Ottoman armies, the area became rather deserted, so Austria encouraged the settlement of Serbs, Germans, Hungarians, Czechs, Slovaks and Rusyns/Ukrainians and other Slavs in the Military Frontier, creating an ethnic patchwork.
The negative effects of feudalism escalated in 1573 when the peasants in northern Croatia and Slovenia rebelled against their feudal lords over various injustices such as unreasonable taxation or abuse of women in the Croatian and Slovenian peasant revolt. Ambroz Matija Gubec and other leaders of the mutiny raised peasants to arms in over sixty fiefs throughout the country in January 1573, but their uprising was crushed by early February. Matija Gubec and thousands of others were publicly executed shortly thereafter, in a rather brutal manner in order to set an example for others.
After the Bihać fort finally fell to the army of the Bosnian vizier Hasan Pasha Predojević in 1592, only small parts of Croatia remained unconquered. The remaining 16,800 km² where around 400,000 inhabitants lived were referred to as the "remnants of remnants of the once great and renowned Kingdom of Croatia" (Latin: reliquiae reliquiarum olim magni et inclyti regni Croatiae).
Kingdom of Croatia (Habsburg)