The balance of powers on Europe’s eastern frontiers was undergoing a transition in the middle of the 15th century. To the north, Muscovy was beginning to outrival the Tatar khanates: in the 1480s, Ivan the Great would repulse the Golden Horde, and install a puppet Khan of Khazan. To the south, the Ottoman threat was all consuming, following the fall of Constantinople in 1453. The Ottoman sultan, Murad II, had gone on to occupy Greece and the southern Balkans but the kingdom of Hungary, under General John Hunyadi and his son, Matthew Corvinus, offered redoubtable defence and, for the duration of the century at least, kept the Turks at bay. The joint kingdom of Poland and Lithuania, under Casimir IV Jagiellon, held impressive territories, especially after its defeat of the Teutonic Knights in the Thirteen Years' War (1454–66), which led to the absorption of western Prussia.