Duchy of Westphalia
In 1736, the Landgraves of Hesse-Darmstadt inherited the estates of the extinct Counts of Hanau-Lichtenberg, again contested by their Kassel cousins. Hesse-Darmstadt gained a great deal of territory by the secularizations and mediatizations authorized by the "Reichsdeputationshauptschluss" of 1803. Most notable was the acquisition of the Duchy of Westphalia, formerly owned by the Prince-Archbishop of Cologne, as well as territories from the Prince-Archbishop of Mainz and the Prince-Bishop of Worms.