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John III, Byzantine emperor of Nicaea
John III (John Ducas Vatatzes) (do͝oˈkəs vətătˈzēz), d. 1254, Byzantine emperor of Nicaea (1222–54), successor and son-in-law of Theodore I. He extended his territory in Asia Minor and the Aegean islands but failed (1235) to take Constantinople from the Latins, although he was aided by Ivan II of Bulgaria. Subsequently Ivan, the Cumans, and the Latins of Constantinople allied themselves against John, who held his own. John joined the Turks against the Mongol invaders. He annexed Salonica (Thessaloníkai) in 1246 and reduced the despotat of Epirus to vassalage, thus nearly recovering the territories of the Byzantine Empire. He maintained close relations with the German emperor, Frederick II, whose daughter he married. During his reign the empire flourished. He was succeeded by his son Theodore II.
John III, king of Poland
John III (John Sobieski) (sôbyĕˈskē), 1624–96, king of Poland (1674–96), champion of Christian Europe against the Ottomans. Born to an ancient noble family, he was appointed (1668) commander of the Polish army. He defeated (1673) the Ottomans at Khotin shortly after the death of King Michael, and in 1674 he was elected to succeed Michael. John's plans to recover East Prussia led him to conclude alliances with France (1675) and Sweden (1677) against Frederick William of Brandenburg (the Great Elector). However, the emphasis of his foreign policy changed when Sultan Muhammad IV and the Hungarians under Thököly advanced against Austria. Realizing the danger to all Europe, John allied (1683) with Holy Roman Emperor Leopold I and, leading combined imperial and Polish forces, raised the siege of Vienna and defeated the much larger Ottoman army under Kara Mustapha. Despite Leopold's ungrateful reception, John continued his campaign and pursued the Ottomans into Hungary. In 1684 he formed a Holy League with the pope, the emperor, and Venice. In 1686 he made a treaty with Russia that confirmed Russian suzerainty in E Ukraine. However, John's attempts (1684–91) to secure access to the Black Sea by wresting Moldavia and Walachia from the Ottoman Empire were unsuccessful. His loss of military prestige encouraged the nobles to oppose him at home. John's death, followed by the choice of the elector of Saxony as King Augustus II of Poland, marked the virtual end of Polish independence.
John III, king of Portugal
John III (John the Fortunate), 1502–57, king of Portugal (1521–57), son of Manuel I. His reign saw the Portuguese empire at its apogee. The great Asian possessions were extended by further conquest, and systematic colonization of Brazil was begun. However, in Portugal itself decadence had set in with the decline of both agriculture and the population. Portugal's African exploits were abandoned, but many black slaves were brought into the country. The Inquisition was introduced (1536) by John, who was devoted to the clerical party. The court was corrupt, though the king was not. Literature flourished early in his reign, but Portugal was falling into the stagnation that characterized the disastrous reign of Sebastian, who succeeded him.
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1. 1507--57, king of Portugal (1521--57): his reign saw the expansion of the Portuguese empire overseas but the start of economic decline at home
2. surnamed Sobieski. 1624--96, king of Poland (1674--96). He raised the Turkish siege of Vienna (1683)
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