The Habsburg-Ottoman conflict in the 16th century presented Austria and the Holy Roman Empire with a formidable eastern challenge. Following the division of Hungary after the Battle of Mohács in 1526, Sultan Suleiman the Magnificent launched numerous campaigns to seize control of Hungarian territories, clashing frequently with Ferdinand I and Charles V of Austria. The Habsburg rulers struggled with financial pressures, introducing the "Turkish Tax" to support Austria's defense and frequently relying on borrowed funds, often from powerful families like the Fuggers. Nonetheless, this revenue was insufficient, and Habsburg forces remained vastly outnumbered by the Ottoman military.
In 1529, Suleiman led a massive force to Vienna, resulting in a tense siege. Though the Ottomans were initially successful in reclaiming Habsburg-held territories, poor weather and the determination of Vienna's defenders ultimately forced them to withdraw. Later, in 1532, Suleiman advanced again, targeting Vienna but detouring to Kőszeg, where the city’s small garrison held its ground, forcing the Ottomans into another retreat. The Peace of Adrianople temporarily halted hostilities, although border skirmishes continued in the so-called "Little War" as both sides vied for control of Hungary.
Austria’s struggle to fund defenses highlighted Hungary’s economic importance within the Habsburg Empire. With Hungary split into Royal Hungary under Habsburg control, Ottoman Hungary, and the Principality of Transylvania, the region became a vital financial source and a persistent battleground. Despite the peace, smaller conflicts continued, with further sieges at Eger and various strongholds along the Hungarian border.
Meanwhile, in the Mediterranean, the Ottomans expanded their naval power, seizing key Christian outposts like Rhodes and challenging European naval dominance. The 1538 Battle of Preveza saw the Ottomans secure supremacy over the Holy League in the region. Charles V's later attempts to secure North Africa were met with mixed success, signaling the increasing power of the Ottoman fleet and marking a significant shift in the regional balance of power.
By the end of this period, Austria found itself locked in a precarious balance: holding Ottoman forces at bay yet unable to reclaim lost Hungarian lands fully, while managing the constant threat of Turkish incursions and financial strain. The uneasy peace would persist until the Long Turkish War of 1593, but the impact of these conflicts reshaped Austria's eastern borders, influenced its finances, and reinforced the urgency of alliances and military modernization for the Habsburgs.