 His troops from there marched to Oldenburg in Holstein, where he was almost completely wiped out in the Battle at the Oldenburg Gulley by an imperial army under Heinrich Schlik and had to surrender on 24 September 1627.In October, George Frederick resigned from the Danish service, after a dispute with the Danish king, who wanted to bring the issue before a court martial.George Frederick retired to his home in Strasbourg and devoted himself mainly to the study of religious literature.