Rantzau was born at Deutsch-Nienhof in
Schleswig-Holstein. He studied at the
University of Wittenberg. A distant relative of
Johan Rantzau, Daniel Rantzau was raised in Holstein, and received a solid academic education but preferred a military career. At the start of the
Northern Seven Years' War, Rantzau was a sub-commander with the rank of colonel but he distinguished himself in some minor struggles during the first fruitless years. In 1565, he was promoted to
commander-in-chief, but his position was weak at the start due to a lack of results on the battlefield. However, in December of the same year Rantzau defeated the Swedish army during the
Battle of Axtorna, an event which strengthened his position. During the following years, he successfully ravaged Swedish areas and established himself as the most able Danish military leader in spite of the lack of a breakthrough. However, a standing conflict about the pay of the soldiers created serious friction between the Danish noble officers and
Peder Oxe, the
Steward of the Realm. From 1567 to 1568, Rantzau carried off what is still considered his main military exploit, his Winter Campaign (
Vinterfälttåget) through
Småland and
Östergötland. During the campaign, he defeated some minor Swedish armies and after having given up an attack on
Stockholm, saved his whole army during a risky but successful retreat across the frozen lake
Sommen. The campaign had no real military results but shook the Swedish defense. In November 1569, during an attack on Swedish-occupied
Varberg Fortress in
Halland, Rantzau was killed by a cannonball. ==Legacy==