Rantzau was born at the castle of Steinburg near Itzehoe into nobility. His family had come into the service of the Danish king after the union between Denmark and the duchies of Schleswig and Holstein, but he was loyal to the rulers of the latter. From his early years he sought a military career and was educated an officer and a lansquenet, but at the same time he also acted as an important political advisor of the duke.
When King Christian II of Denmark in 1523 was overthrown by Frederick I in 1523, Rantzau lead Frederick’s army of conquest. He became a member of the Danish Privy Council as well as governor of the duchies and was the most important of the king’s non-Danish advisors. At the same time he emerged a squire of Holstein, making the manor house of Breitenburg his entailed estate. Among his military missions was his fight against the Scanian peasant rebellion of 1525 that was bloodily crushed. During these years he also became a devote Protestant, working together with his Danish colleagues on advancing the Lutheran cause.
Rantzau became especially notable due to his participation in the Count’s Feud from 1534-1536. Together with the Holstein nobility, he supported Christian III in spite of the latter’s desperate situation. An attempt of conquering Funen in 1534 ended in a defeat and a humiliating retreat, but in the same year Rantzau crushed Skipper Clement's peasant rebellion in Jutland and secured the peninsula for the king. Next year he successfully conquered Funen, defeating Count Christopher of Oldenburg’s army at Øksnebjerg and finally leading the siege of Copenhagen that ended with the triumph of Christian III.
After the war, Rantzau continued being the king’s general and advisor, but he was pushed into the background in Denmark while concentrating on Holstein affairs. In 1545 he resigned as the governor of Schleswig and Holstein in protest against the threefold division of the duchies between King Christian III and his brothers John the Elder and Adolf the year before. However, he went back into active service in 1559 as the leader of the conquest of Dithmarschen, which he managed both recklessly and quickly.
As an outstanding figure of military history of the 16th century, Rantzau has been both lauded and blamed. Earlier historians have normally called him a brilliant general, loyal to the royal house of Denmark, a man of clear strategic and tactic gifts and ability of quick solutions. However, liberal and national historians, and especially class oriented historians, i.e. Marxists, often stress him as a representative of militarism and squire interests criticising him as a ”peasant’s butcher” – in many ways a parallel to the Finnish Mannerheim debate.
Rantzau’s son Heinrich Rantzau (1526–1598) was an outstanding Holstein cattle lord, governor, and squire of cultural and literary interests. His biography of his father is the main source of the latter’s life.
- Dansk Biografisk Leksikon, vol.11, Copenh. 1982.
- Politikens Danmarkshistorie, vol 5, by Johan Hvidtfeldt. Copenh. 1963.
- Politikens Danmarkshistorie, vol 6, by Svend Cedergreen Bech, Copenh. 1963.