Duchy of Oldenburg

The Duchy of Oldenburg — named after its capital, the town of Oldenburg — was a state in the north-west of present-day Germany. The counts of Oldenburg died out in 1667, after which it became a duchy until 1810, when it was annexed by the First French Empire. It was located near the mouth of the River Weser.

When the main lineage of the House of Oldenburg died out in 1667 with Anthony Günther, Count of Oldenburg, it fell to the Frederick III of Denmark of the line of the Dukes of Holstein-Gottorp, who married Grand Duchess Anna Petrovna of Russia, daughter of Peter the Great. Another, his first cousin, Frederick August I, became Duke of Oldenburg in 1774. One of his brothers, Adolf Frederick, became King of Sweden. Another brother, Prince Georg Ludwig of Holstein-Gottorp, was father of Peter I, who became Grand Duke of Oldenburg in 1823. Subsequent Rulers of Oldenburg were all his descendants.

Wikipedia