Since the fall of Constantinople in 1571, the Ottoman Empire had expanded into Europe. In 1683, Ottoman forces under military leader and grand vizier Kara Mustafa Pasha invaded Austria and besieged Vienna. A huge relief army of Poles, Germans and Austrian allies under King Jan III Sobieski of Poland overcome them and they fled the city. A new Holy League, comprising the Holy Roman Empire, Polish-Lithuanian Commonwealth, Venetian Republic and Russian troops, was established to oppose Ottoman expansion. A series of battles between this Christian alliance and the Turks culminated in Ottoman defeat at the Battle of Zenta in 1697 and the subsequent Treaty of Karlowitz, ending Ottoman control over large areas of central Europe. Yet the Ottomans engaged in war with Russia (1710–11) and Venice (1714–18), prompting the Austrians to intervene. The Turks were defeated at Peterwardein in 1716 and the Austrians took Belgrade in 1717. The 1718 Treaty of Passarowitz made the Danube the border between Islam and Christianity.
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