Frederick III of Holstein-Gottorp

Frederick III of Holstein-Gottorp was a Duke of Holstein Gottorp and briefly Sovereign Duke of Schleswig-Holstein, member of the Oldenburg Dynasty ruling in Denmark-Norway.

Early Life
Frederick was the elder son of Johann Adolf, Duke of Holstein-Gottorp, and Augusta of Denmark. Barely nineteen when deemed of ruling age, the Duke had ambitious plans to increase Holstein's sea trade capability. In 1621 he founded his namesake city Friedrichstadt, part of a network of trading harbors on the North Sea.

Danish Intervention
By the time of Frederick of Denmark's intervention, the Duke was able to supply his kinsman with provisions. Otherwise, he kept neutral, fearing an Imperial retaliation against his lands.

Schleswig War
However, he would abandon his neutrality in the wake of the Schleswig War. In 1626, following an Imperial Ban, the King of Denmark was stripped of his titles in Schleswig and Holstein. Frederick III would claim them as sovereign, a fact that would enrage the other partitioned-off line of the House, the Sondenburg line. His forces would aid Hans Georg von Arnim's advance through the peninsula, after which they returned to their quarters.

Danish-Holstein War
His fortunes would turn on him in early 1630. Emperor John George I of Saxony refused to continue the war effort against Denmark, which had in the meantime peaced out with Sweden at Knared. In the Treaty of Rostock, Denmark was restored in its Imperial territories, reversing Frederick's gains. The Duke refused to hand the entirety of Holstein back, sparking the Danish-Holstein War.