During the next fifteen years, he fulfilled his duty of establishing peace in the border area so well that he was titled Duke of Holstein (Hertug af Holsten) and became a vassal of the Holy Roman Empire.
Selama lima belas tahun kedepan, ia memenuhi tugasnya membangun perdamaian di wilayah perbatasan dengan baik sehingga ia digelari Adipati Holstein (Hertug af Holsten) dan menjadi vasal Kekaisaran Romawi Suci.