During the Northern Seven Years' War, Kaas remained in Copenhagen and helped negotiate with Sweden in Roskilde.

[5] In June 1587 when Frederick II had toothache, Kaas met the Scottish ambassadors Patrick Vans and Peter Young who wanted to discuss the marriage of James VI to a Danish princess.

During this time, he dealt with many issues, such as the influence wielded by the dowager queen Sophia and her father Duke Ulrich III of Mecklenburg-Güstrow.

[8] On 12 December 1591 he signed the autograph book of Dietrich Bevernest, writing, "Fortuna fugacior undis.

"[9] In 1593, Kaas helped emancipate the duchies of Schleswig-Holstein from the Holy Roman Empire and secure the rule over them of Frederick's successor, Christian IV.

On his deathbed in 1594, Kaas called Christian IV in order to advise him on government, saying: Your grace Lord Father, holy remembrance, I promised to his utmost, that I with all power, counsel and faithfulness should ensure that the crown came upon your head.

Take therefore the kingdom treasures of God himself, bears the crown with Price and glory reigns spire with wisdom and grace, bring the sword of justice and power and keeps the orb lay with counsel and prudence.