The duchy had its origins in the medieval Burgraviate of
Altenburg in the Imperial
Pleissnerland (Terra Plisensis), a possession of the Wettin
Margraves of Meissen since 1243. Following the
partition of Leipzig in 1485, Altenburg fell to
Ernst, Elector of Saxony, the progenitor of the
Ernestine Wettins. After the
Capitulation of Wittenberg in 1547, the area around Altenburg went to the
Albertine branch, but it was transferred back to the Ernestine by the in 1554, and then to the Duchy of
Saxe-Weimar following the in 1572. File:Saxony (Division of Leipzig) - DE.png|Altenburg within Ernestine domains (red) upon the
Treaty of Leipzig (1485) File:Saxony after the Capitulation of Wittenberg (1547) - DE.png|Transfer of Altenburg to Albertine domains (striped) upon the
Capitulation of Wittenberg (1547) File:Saxony after the Treaty of Naumburg - DE.png|Transfer of Altenburg back to Ernestine domains (striped) upon the
Treaty of Naumburg (1554) When Johann Wilhelm's son and successor
Friedrich Wilhelm I died in 1602, the Duchy of Saxe-Weimar passed to his younger brother
Johann II. In 1603 Frederick William's eldest son
Johann Philipp received the newly created
Duchy of Saxe-Altenburg as compensation. It was an
Imperial State in its own right, with a vote in the
Reichstag, for much of the 17th century until the extinction of its ruling line in 1672 when it was inherited by
Ernest I the Pious, the Duke of
Saxe-Gotha, who had married the heiress. Saxe-Altenburg thereafter remained part of
Saxe-Gotha-Altenburg until the extinction of that house in 1825, when Gotha and Altenburg were divided up, with Gotha going to the Duke of
Saxe-Coburg-Saalfeld and Altenburg to the Duke of
Saxe-Hildburghausen, who in exchange gave up Hildburghausen to the Duke of
Saxe-Meiningen. This family ruled the duchy until the end of the monarchies in the course of the
German Revolution of 1918–19. The succeeding
Free State of Saxe-Altenburg became part of the new
State of Thuringia when it formed in 1920. ==Dukes of Saxe-Altenburg==