effort of Sava, the country's patron saint, and in 1346 it was raised to the Patriarchate. Monuments of the Nemanjić period survive in many monasteries (several being World Heritage sites) and fortifications. During these centuries the Serbian state (and influence) expanded significantly. The northern part (modern Vojvodina), was ruled by the Kingdom of Hungary. The period after 1371, known as the Fall of the Serbian Empire saw the once-powerful state fragmented into several principalities, culminating in the Battle of Kosovo (1389) against the rising Ottoman Empire. The Ottomans finally conquered the Serbian Despotate in 1459. The Ottoman threat and eventual conquest saw massive migrations of Serbs to the west and north. Ottoman and Habsburg rule In all Serbian lands conquered by the Ottomans, the native nobility was eliminated and the peasantry was enserfed to Ottoman rulers, while much of the clergy fled or were confined to the isolated monasteries. Under the Ottoman system, Serbs, as well as Christians, were considered an inferior class of people and subjected to heavy taxes, and a portion of the Serbian population experienced Islamization. Many Serbs were recruited during the devshirme system, a form of slavery in the Ottoman Empire, in which boys from Balkan Christian families were forcibly converted to Islam and trained for infantry units of the Ottoman army known as the Janissaries. The Serbian Patriarchate of Peć was extinguished in 1463, but reestablished in 1557, providing for limited continuation of Serbian cultural traditions within the Ottoman Empire, under the Millet system. After the loss of statehood to the Ottoman Empire, Serbian resistance continued in northern regions (modern Vojvodina), under titular despots (until 1537), and popular leaders like Jovan Nenad (1526–1527). From 1521 to 1552, Ottomans conquered Belgrade and regions of Syrmia, Bačka, and Banat. Continuing wars and various rebellions constantly challenged Ottoman rule. One of the most significant was the Banat Uprising in 1594 and 1595, which was part of the Long War (1593–1606) between the Habsburgs and the Ottomans. The area of modern Vojvodina endured a century-long Ottoman occupation before being ceded to the Habsburg Empire, partially by the Treaty of Karlovci (1699), and fully by the Treaty of Požarevac (1718). As the Great Serb Migrations depopulated most of southern Serbia, the Serbs sought refuge across the Danube River in Vojvodina to the north and the Military Frontier in the west, where they were granted rights by the Austrian crown under