In 1630, Sweden intervened into the Thirty Years' War on the side of the Protestants. On 27 July, Magdeburg's former administrator Christian Wilhelm von Brandenburg slipped into the city, seizing back power. Christian Wilhelm immediately declared his allegiance for Sweden. Falkenberg was appointed to the rank of Commandant and sent to Magdeburg, which he managed to enter in October by disguising himself as a sailor. He then presented the city's council with a letter reassuring them of Sweden's support in their struggle against the Holy Roman Empire and the Catholic League. Soon afterwards, Imperial general Gottfried Heinrich Graf zu Pappenheim chased Magdeburg's militia into the city, imposing a siege. In the meantime, Falkenberg became the head of Magdeburg's garrison, organized a recruitment drive and strengthened the fortifications. The majority of Magdeburg's population appeared reluctant as they have grown tired of the war, the exception being the local radical Protestant clergy.