Croatian-Slavonian theater in Great Turkish War, concerns military operations undertaken during Great Turkish War of 1684-1689 by the forces of Holy League against the Ottoman Empire on territories of Croatia, Slavonia and Dalmatia. The war was concluded by Treaty of Karlowitz in 1699, which significantly eased off the Ottoman grip off Croatia.
Prelude
Croatian-Ottoman Wars
Following the Ottoman conquest of Kingdom of Bosnia in 1463, the territories of Slavonia, Croatia and Dalmatia came under ever increasing Ottoman pressure. Initially, armies led by Croatian nobles resisted frequent akinji and martolos incursions, and even scored some victories such as the Battle of Una and Battle of Vrpile Pass. However, the regular attacks which usually came once a year, eventually proved to be too much for Croatia to handle alone and they culminated in Croatian defeat at Battle of Krbava Field in 1493, where much of Croatian nobility was killed. Lack of funds and poor help from the weak Hungarian kings of Jagellonian dynasty resulted in ever increasing depopulation of Croatian lands, burdened by constant state of warfare. As a result of Ottoman conquests, center of the Croatian medieval state gradually moved northwards into Slavonia (Zagreb). Since Slavonian territory also kept shrinking due to Ottoman conquests, the political breaking point happened on 1 September 1558, when united Croatian-Slavonian parliament was held in Zagreb, which became a permanent political state in the future. Due to migrations of Croatian nobility and common people, "the Croatian name", also moved northwards in what was once medieval Slavonia.
After Hungarian defeat in Battle of Mohacs in 1526 and ensuing succession crisis inside the Hungarian-Croatian kingdom, the Ottomans made use of this dissolution, by further taking large parts of Hungary, Slavonia, Croatia and Dalmatia in first half of the 16th century. The Croatian lands were thus reduced to "remnants of the remnants" - a rather small part of western parts of medieval Slavonia and Croatia. After Croatia joined Habsburg Monarchy on Diet of Cetingrad in 1527, its depopulated territories were further taken out of Croatian jurisdiction by Habsburg decree, through formation of Military Frontier under command of Imperial War Council in Graz. Nonetheless, the Ottoman conquest of Croatian lands was mostly halted by their defeat in Battle of Sisak in 1593.
The Siege of Vienna 1683 and Formation of Holy League
The Vasvár peace, the twenty year long period of peace established by the Vasvár peace treaty in 1664, was due to expire in twenty years, and weakened Ottoman Empire, decided to renew its hostilities against the Habsburg Monarchy. In the year 1683, a massive army was assembled and sent off across Ottoman Balkan and Hungarian territories in order to attack and besiege Vienna. The siege of Vienna in 1683 ended in disaster for the Ottomans as their besieging army was routed near Vienna by the relief forces of Polish king Jan III Sobieski. Following the Ottoman defeat, an anti-Ottoman alliance sponsored by the Pope, named the "Holy League" was formed. The League comprised the Habsburg Monarchy, Poland and Venice, and its goal was pushing the Ottomans out of Europe.
Croatian preparations
According to Croatian historian Tadija Smičiklas, by the end of 1682, Croatian nobility was well aware of Ottoman intentions to attack Vienna again. For example, back in March 1682, Croatian friar Luka Ibrišimović sent letters to bishop of Zagreb, informing him of increased Ottoman activities in Slavonia such as: collecting food and augmenting fortifications and bridges. Same year in May, he sent another report of Ottomans making lists of all available soldiers in Slavonia and stockpiling their large cannons in Osijek. With that in mind, between 1682 and 1683 Croats began with their own preparatory measures such as intense communication with emperor Leopold, Styrian and Carniolan nobility, as well as the Pope; who even sent some financial aid. The grad vizier Kara Mustafa apparently also dispatched letters, trying to persuade Croatians to join his army in attack on Vienna, but these were rejected.
While anticipating impending Ottoman strike on Vienna, Croatian army remained deployed on borders of Croatia, Styria and Carniola, should Ottomans decide to swing southwards during their offensive on Habsburg capital. Croatian-Slavonian Parliament assembled in May 1683 in Varaždin in order to discuss the final preparations for impending Ottoman strike.