For some years, he fought in Germany and Italy, and also took part in the Danish conquest of Dithmarschen in western Holstein during 1559.

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.

[4] From 1567 to 1568, Rantzau carried off what is still considered his main military exploit, his Winter Campaign (Vinterfälttåget) through Småland and Östergötland.