When Leopold I became heir apparent to the Habsburg lands his father, Ferdinand III, made him king of Hungary (1655) and Bohemia (1656). Upon his father’s death, he inherited Austria and, despite opposition from France, became Holy Roman Emperor in 1658. Habsburg power was consolidated in central and eastern Europe, but not without threat. The Peace of Olivia (1660) secured Bohemia, but France continued to pose a military risk, and Austria was the easternmost line of defense against the Ottoman-Turks. The Ottoman siege of Vienna in 1683 was overcome, followed by a series of successful counter-campaigns, resulting in the Treaty of Karlowitz (1699) when Austria received large areas of Hungary, Croatia, Transylvania and Slovenia from the Ottomans. Elsewhere, the Thirty Years’ War had left much of Brandenburg scarred by warfare. Frederick William, Elector of Brandenburg (r. 1640–88) reduced the authority of the estates, acquired Pomerania and its strategic ports, and introduced absolutism. Austria under Leopold I emerged as a great European power; Frederick William laid the foundations for powerful Prussia and its future monarchy.
— OR —