The ancient Thuringians, a Germanic tribe occupying central Germany between the Elbe and the Danube, were conquered by the Franks during the 6th cent. a.d. and were converted (8th cent.) to Christianity by St. Boniface. Charlemagne made Thuringia a march (frontier country) against the Slavs in the 9th cent., but it passed under the control of the Saxon dukes in the 10th cent.

In the 11th cent. the landgraves of Thuringia, with their seat at the celebrated Wartburg, emerged as princes of the Holy Roman Empire and ruled over much of the territory that is modern Thuringia. When Landgrave Louis IV died (1227) on a Crusade, Louis's widow, St. Elizabeth of Hungary, was expelled by his brother and successor, Henry Raspe, who later was antiking to Conrad IV. Although the succession to Thuringia was long contested after Henry's death in 1247, the major part eventually fell to the house of Wettin, i.e., to the margraves of Meissen, who in 1423 became electors of Saxony.

The division (1485) of the Wettin lands left most of the Thuringian territories in the hands of the Ernestine branch of the family, which also received the electoral title. Thuringia was split, under the Ernestines, into several duchies (see Saxe-Altenburg; Saxe-Coburg; Saxe-Gotha; Saxe-Meiningen; Saxe-Weimar). Principalities situated in Thuringia but not ruled by any of the branches of the Ernestine line were those of Reuss and Schwarzburg. Among the Ernestine duchies (which underwent several redivisions in the 17th, 18th, and 19th cent.) the most important, both politically and culturally, was Saxe-Weimar-Eisenach (see under Saxe-Weimar).

All the Thuringian territories except Saxe-Meiningen sided with Prussia in the Austro-Prussian War of 1866. The Thuringian states had been members of the German Confederation from 1815; they joined the North German Confederation in 1866 and the German Empire in 1871. Their rulers were expelled in 1918, and in 1920 the state of Thuringia was founded under the Weimar Republic by the union of Saxe-Coburg-Gotha (without the city of Coburg, which went to Bavaria), Saxe-Weimar-Eisenach, Saxe-Altenburg, Saxe-Meiningen, the two sister principalities of Reuss, and the two sister principalities of Schwarzburg.

As constituted in 1946 under Soviet military occupation, Thuringia consisted of the prewar state of Thuringia with the addition of former Prussian enclaves and border areas, notably Erfurt and Mühlhausen. In 1952 the state was abolished as an East German administrative unit, and Thuringia was split into the districts of Erfurt, Suhl, and Gera. It was reintegrated as a state shortly before German reunification in Oct., 1990. It is the smallest but most densely populated of the new German states. The heavily industrial region began to experience economic hardship by the 1990s; many of its largest industrial concerns went out of business.