Duchy of Oldenburg

The Duchy of Oldenburg, named for its capital town, was a state of north-west Germany whose counts are known from Elimar I around 1100. The line served, and sometimes defied, the dukes of Saxony, until Frederick I's dismemberment of Saxony in 1180 made them princes of the empire, and through the thirteenth century they fought the Frisians and the bishops of Münster and Bremen to enlarge their land, with Delmenhorst repeatedly split off for younger sons. In 1440 Christian of Oldenburg inherited the county and went on to the thrones of Denmark, Norway and Sweden, founding the royal fortunes of the house. On Count Anthony Günther's death in 1667 the county passed to Frederick III of Denmark of the Danish Oldenburg line, and in 1773 the Treaty of Tsarskoye Selo transferred it to Frederick August I of Holstein-Gottorp, after which the county became a duchy. Annexed by Napoleonic France in 1810, it returned in 1815 as a grand duchy, with Peter I taking the grand-ducal title in 1823, and it ended with the German monarchies in 1918, while cadets of the house went on to reign in Denmark, Norway, Sweden, Greece and Russia.