By the 16th century, the Ottomans had become a serious threat to the European powers, with Ottoman ships sweeping away Venetian possessions in the Aegean and Ionian seas and Ottoman-supported Barbary pirates seizing Spanish possessions in the Maghreb. The Protestant Reformation, the French–Habsburg rivalry and the numerous civil conflicts of the Holy Roman Empire served as distractions to the Christians from their conflict with the Ottomans. Meanwhile, the Ottomans had to contend with the Persian Safavid Empire and to a lesser extent the Mamluk Sultanate, which was defeated and fully incorporated into the empire.
Initially, Ottoman conquests in Europe made significant gains with a decisive victory at Mohács reducing around one third (central) part of Kingdom of Hungary to the status of an Ottoman tributary. Later, the Peace of Westphalia and the Spanish War of Succession in the 17th and 18th centuries respectively left the Austrian Empire as the sole firm possession of the House of Habsburg. Following the Siege of Vienna in 1683 the Habsburgs were able to assemble a large coalition of European powers known as the Holy League, allowing them to effectively combat the Ottomans and to regain control over Hungary. The Great Turkish War ended with the decisive Holy League victory at Zenta. The wars came to an end following Austria's participation in the war of 1787-1791, which Austria fought in alliance with Russia. Intermittent tension between Austria and the Ottoman Empire continued throughout the nineteenth century, but they never again fought each other in a war and ultimately found themselves allied in World War I, in the aftermath of which both empires were dissolved.
Historians have devoted most of their attention to the second siege of Vienna of 1683, depicting it as a decisive Austrian victory that saved Western civilization and began the fall of the Ottoman Empire. However more recently historians have taken a broader perspective noting that the Habsburgs at the same time resisted internal separatist movements, and were battling Prussia and France for control of central Europe. The key advance made by the Europeans was an effective combined arms doctrine in which the infantry and artillery, supported by the cavalry, cooperated together to be triply effective. Nevertheless, the Ottomans were able to maintain military parity with the Habsburgs until the middle of the eighteenth century. Historian Gunther E. Rothenberg has emphasized the non-combat dimension of the conflict, whereby the Habsburgs built up military communities that protected their borders and produced a steady flow of well-trained, motivated soldiers.
While the Habsburgs were occasionally the Kings of Hungary and Emperors of the Holy Roman Empire (and almost always that of the Holy Roman Empire after the 15th century), the wars between the Hungarians and the Ottomans included other Dynasties as well. Naturally, the Ottoman Wars in Europe attracted support from the West, where the advancing and powerful Islamic state was seen as a threat to Christendom in Europe. The Crusades of Nicopolis (1396) and of Varna (1443–44) marked the most determined attempts by Europe to halt the Turkic advance into Central Europe and the Balkans.
For a while the Ottomans were too busy trying to put down Balkan rebels such as Vlad Dracula. However, the defeat of these and other rebellious vassal states opened up Central Europe to Ottoman invasion. The Kingdom of Hungary now bordered the Ottoman Empire and its vassals.
After King Louis II of Hungary was killed at the Battle of Mohács in 1526, his widow Queen Mary fled to her brother the Archduke of Austria, Ferdinand I. Ferdinand's claim to the throne of Hungary was further strengthened by his marriage to Anne, the sister of King Louis II and the only family member claimant to the throne of the shattered Kingdom. Consequently, Ferdinand I was elected King of Bohemia, and at the
Diet of Pozsony he and his wife were elected King and Queen of Hungary. This clashed with the Turkish objective of placing the puppet John Szapolyai on the throne, thus setting the stage for a conflict between the two powers.