In the 15th century, much of what is now the German state of Thuringia, including the area around Eisenach, was in the hands of the Wettin dynasty, since 1423 Prince-electors of Saxony. In 1485, the Wettin lands were divided according to the Treaty of Leipzig, with most of the Thuringian lands going to Elector Ernest of Saxony and his descendants. The Ernestine Wettins also retained the title of Elector. However, when Ernest's grandson John Frederick the Magnanimous revolted against Emperor Charles V during the Schmalkaldic War, he was defeated at the 1547 Battle of Mühlberg and deprived of the electorate in favour of his Wettin cousin Maurice. According to the Capitulation of Wittenberg he was only allowed to retain the lands in Thuringia.
For the next three centuries the Ernestine lands were divided whenever the dukes had more than one son to provide for, and re-combined when they died without direct heirs, but all of the lands stayed in the Ernestine branch of the Wettin family. All descendants of John Frederick the Magnanimous in the male line bore the title "Duke of Saxony", whether or not they actually ruled any territory. Brothers sometimes ruled jointly, but usually there was a division of territory if there was more than one son to inherit. As a result, the Duchy of Saxe-Eisenach was separated from and subsumed into other Ernestine duchies several times. The actual territories included in the duchy changed with each creation, but always with the town of Eisenach as the core.
Duchies of Saxe-Eisenach
The first Duchy of Saxe-Eisenach was created in 1596, after the banned Duke John Frederick II had died in captivity and his surviving sons had come of age. Their Duchy of Saxe-Coburg-Eisenach was split, whereby the younger John Ernest became Duke at Eisenach, while the elder John Casimir took his residence at Coburg. When in 1633 Duke John Casimir died without issue, the Wettin line in Saxe-Coburg died out, and John Ernest inherited it. Nevertheless, he himself also died heirless in 1638, and his territories were split between Saxe-Weimar and Saxe-Altenburg, which had itself been separated from Saxe-Weimar in 1603.
Eisenach City Palace, finished in 1748
In the course of the partition of the Saxe-Weimar lands among the sons of late Duke John II in 1640, the eldest brother William of Saxe-Weimar gave the re-established Duchy of Saxe-Eisenach to his younger brother Albert IV, while the youngest Ernest received the Duchy of Saxe-Gotha. However, Duke Albert died without heirs in 1644, and Saxe-Eisenach was then divided between Saxe-Gotha and Saxe-Weimar, ruled by his brothers.
For nearly 20 years the residence of Eisenach was part of Saxe-Weimar. However, when Duke Wilhelm of Saxe-Weimar died in 1662, he left four children: John Ernest, Adolf William, John George and Bernard. The second eldest, Adolf William, received Eisenach. He had to share this, however, with his younger brother John George, who finally accepted the receipt of an income from the duchy of Saxe-Eisenach and made his residence in the small town of Marksuhl. Adolf William had five sons, but the first four died soon after birth. In 1668 he died, just before of the birth of his fifth son, Willam Augustus, who became the new Duke of Saxe-Eisenach from his birth, under the guardianship of his uncle John George. A sickly boy, he died in 1671 at only two years old, and John George became Duke of Saxe-Eisenach.
Saxe-Eisenach assumed its final shape in 1672, following the death of Frederick William III of Saxe-Altenburg and the partition of his lands. The line of Johann Georg I ruled Saxe-Eisenach for 69 years, until Duke Wilhelm Heinrich died heirless in 1741. Duke Ernest Augustus I of Saxe-Weimar, Wilhelm's second cousin, inherited Saxe-Eisenach; he and his successors ruled Saxe-Weimar and Saxe-Eisenach in personal union until 1809, when the duchies were formally merged into the Duchy of Saxe-Weimar-Eisenach.
