He was the second son of
Johann Frederick I, Elector of Saxony, and
Sibylle of Cleves. At the time of his birth, his father still carried the title Elector of Saxony, but he lost it in 1547 after his defeat and capture by the Emperor
Charles V due to his support of the
Protestant Reformation. Johann Frederick was released and forced to adopt the lesser title of duke of Saxony in an area substantially smaller than his former lands in
Thuringia. In 1554, after the death of his father, Johann Wilhelm inherited the duchy of Saxony with his older brother,
Johann Friedrich II, and his younger brother,
Johann Friedrich III. The three brothers divided the duchy: Johann Friedrich II as head of the family took
Eisenach and
Coburg; Johann Wilhelm received
Weimar; and Johann Friedrich III inherited
Gotha. In 1565, however, when Johann Frederick III died without heirs, the two surviving brothers drew up a new treaty that divided his lands. The older brother retained his original lands and occupied Gotha, whereas Johann William retained his lands in Weimar. The partition plan also stipulated that the two brothers should exchange their regions among themselves every three years. This provision was never carried out, however. The political policies of Johann Friedrich II were directed towards recovering the lands and title of elector lost by his father in 1547. He did briefly recover the electorate during the period 1554–1556, but his involvement in political intrigues angered the Emperor
Maximilian II. The Emperor finally imposed the
Reichsacht (Imperial ban) on him, which made him the object of a
Reichsexekution (Imperial police action) in which Johann Wilhelm participated. After a siege of his castle in Gotha, Johann Friedrich was finally defeated in 1566 and spent the rest of his life as an Imperial prisoner. His possessions were confiscated by the Emperor and handed over to Johann Wilhelm, who thereby became the only ruler of the entire duchy of Saxony. Johann Wilhelm soon fell into disfavor with the Emperor, however, when he entered the service of the King
Charles IX of France as a general in his campaign against the
Huguenots (the French kings were the enemies of the
Habsburg emperors). This also alienated his Protestant subjects. Johann Wilhelm was a member of the
House of Wettin, which had served as the
protecting power of
Protestantism in Germany since the time of
Frederick the Wise, yet he allied himself with the Catholic King of France against the Protestants Huguenots. The Emperor played off the two surviving sons of Johann Friedrich II against Johann Wilhelm, and in 1572 the
Division of Erfurt was concluded. The duchy of Saxony was divided into three parts. The older of the two sons of Johann Friedrich II,
Johann Casimir, received
Coburg, and the younger,
Johann Ernst, received
Eisenach. Johann Wilhelm retained only the smaller part of the duchy, the region around
Weimar, but he added the districts of
Altenburg,
Gotha, and
Meiningen to his territories. As a result of the Division of Erfurt, all of the territorial possessions of the House of Wettin, no matter which branch ruled the individual components, became contiguous. The house of
Saxe-Weimar and the first house of
Saxe-Altenburg, which later separated from Saxe-Weimar (see also the
Ernestine duchies), both descend from Johann Wilhelm. ==Marriage and issue==