Duke Henry IV had re-united the Mecklenburg lands under his rule through his inheritance of the former Lordships of Werle and Stargard in 1436 and 1471, respectively. Near the end of his life, Henry IV devoted more and more time to hedonistic luxury, while Magnus and his brothers Albert and John took over the most active share in the business of government.
Francis Otto, Duke of Brunswick-Lüneburg (1530–1559), married Elisabeth Magdalena of Brandenburg, daughter of Joachim II Hector of Brandenburg and Hedwig of Poland. Frederick (1532–1553) Henry III, Duke of Brunswick-Lüneburg (1533–1598) married Ursula of Saxe-Lauenberg, daughter of Francis I, Duke of Saxe-Lauenburg
Nevertheless, the comital Holstein lands south of the Eider River officially remained a mediate fief held by the Ascanian dukes of Saxe-Lauenburg. In 1474 Emperor Frederick III conferred Imperial immediacy to Christian by elevating him to a Duke of Holstein.