 Complete the following phrase:  The changing nature of sultanic authority led to several political upheavals during the 17th century, as rulers and political factions struggled for control over the imperial government. In 1622 Sultan Osman II was overthrown in a Janissary uprising. His subsequent regicide was sanctioned by the empires chief judicial official, demonstrating a reduced importance of the sultan in Ottoman politics. Nevertheless, the primacy of the Ottoman dynasty as a whole was never brought into question. Of seventeenth-century sultans, Mehmed IV was the longest reigning, occupying the throne for 39 years from 1648 to 1687. The empire experienced a long period of stability under his reign, spearheaded by the reform-minded Köprülü family of grand viziers. This coincided with a period of renewed conquest in Europe, conquests which culminated in the disastrous Siege of Vienna in 1683 and the fall from grace of the Köprülü family. Following the battle a coalition of Christian powers was assembled to combat the Ottomans, bringing about the fall of Ottoman Hungary and its annexation by the Habsburgs during the 