The Landgraviate of Hesse-Kassel expanded in 1604 when Maurice, Landgrave of Hesse-Kassel inherited the Landgraviate of Hesse-Marburg from his childless uncle, Louis IV, Landgrave of Hesse-Marburg (1537-1604).
Although it was a fairly widespread practice at the time to rent out troops to other princes, it was the Landgraves of Hesse-Kassel who became infamous for hiring out contingents of their army as mercenaries during the 17th and 18th centuries.