Thuringia (German: Thüringen) was a margravate in the center of the HRE. 1247-64, it fought in the Hessian-Thuringian War of Succession. Sophie of Brabant (who was supported by the Teutonic Order) made sure that Hesse stayed independent and went to her son Heinrich "the Child". ITTL he even got a slightly bigger share, at the expense of Thuringia.
The Wettin division
Heinrich III reigned all of Thuringia, the margravate Meissen and the Palatinate of Saxony. But in 1265, he divided his lands and only kept Meissen and Lower Lusatia, while Thuringia and the Saxon Palatinate went to his son Albrecht II "the degenerate"; his other son Dietrich IV received the Mark Landsberg and Osterland. (Wettin history seems to diverge when Heinrich had no third son in 1273.) In 1288, he died too; Meissen went to Albrecht II, Lower Lusatia to Friedrich III.
1306, the Wettins suffered the loss of Lower Lusatia which went to Roman king Otto IV of Brandenburg. In the years 1335/37, most Wettin lands were united by Friedrich IV; but as soon as 1357, Meissen and Thuringia were separated again, between Diezmann III and Friedrich VI. And 1445, Thuringia was again divided into the lines of Weimar, Altenburg and Coburg. This was no help in the Twenty-Year War, where the Wettin states of Thuringia, Meissen and Osterland only acquired the clerical lands of Meissen and Merseburg, which was why they made war against Brandenburg, too.
In the 16th century, Thuringia slowly consolidated again. 1526, Meissen and the Saxon Palatinate were inherited by Thuringia-Weimar; in 1589, Thuringia-Coburg went to Altenburg; and 1622, Thuringia-Altenburg was inherited by Weimar.
In the years around 1600, peasant uprisings happened. The German nobles repeatedly had raised taxes, which the peasants in Thuringia couldn't pay any more, because in these areas, the peasants used to divide their lands among all kids - so their plots had become smaller and smaller. The revolters demanded a "jubilee" (when all debts were to be cancelled), no lord except emperor, pope and God, liberation of the serfs, election of the clerics by the people, peace among Christians, restitution of their old rights and lower taxes. The uprisings were mixed with religious movements (which were, sadly, often antisemitic). Not too surprisingly, the uprisings were defeated as everywhere else. Those who could, tried their luck elsewhere - some going even to Atlantis.
The Wettins could celebrate another triumph when Georg IV of Thuringia-Weimar was Roman king 1695-99.
Thuringia participated in the French Republican Wars at the monarchist side, not to their luck. In 1783, the French invaded Dresden, and made the Hermunduric Republic of the old duchy of Thuringia-Meissen. The Wettins fled to Prussia, spending their last years in a civil war, until Novorossiya invaded the place and made their end.
After the German Uprising 1818, Thuringia became a part of united Germany.
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