John II (John Casimir), 1609–72, king of Poland (1648–68), son of Sigismund III. He was elected to succeed his brother, Ladislaus IV. The turbulent period of his reign is known in Polish history as the Deluge. The uprising of the Cossacks under Chmielnicki, supported by the khan of Crimea, had begun under his predecessor. John II defeated (1651) the allied Cossack, Tatar, and Ottoman forces, but in 1654 the Cossacks accepted Russian suzerainty over Ukraine, and Czar Alexis promptly invaded Poland. In 1655, Charles X of Sweden nearly overran Poland and was checked only by the successful Polish defense of Częstochowa, which inspired the Poles to renewed resistance. George II Rákóczy, prince of Transylvania, attacked Poland from the south but was defeated. Frederick William of Brandenburg (the Great Elector), originally a Swedish ally, joined (1657) the Polish side in the struggle; in return John recognized his full sovereignty over East Prussia. The fighting in the west was concluded in 1660 (see Oliva, Peace of). War with Russia ended only in 1667, with the cession of the eastern part of Ukraine to the czar. During John's reign the liberum veto (by which any deputy could dissolve the diet and annul its decisions) was greatly abused. The king and his French consort, Louise Marie de Gonzague (widow of Ladislaus IV), were childless; their efforts to nominate a successor evoked several rebellions of the nobles. John abdicated a year after the death (1667) of his queen, and retired to an abbey at Nevers, France. Michael Wisniowiecki was elected his successor; disorder continued during his reign (1668–73), which was followed by that of John III.
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