Hessian War

The Hessian War (German: Hessenkrieg), in its wider sense sometimes also called the Hessian Wars (Hessenkriege), was a drawn-out conflict that took place between 1604 and 1648, sometimes pursued through diplomatic means, sometimes by military force, between branches of the princely House of Hesse, particularly between the Landgraviate of Hesse-Cassel and the Landgraviate of Hesse-Darmstadt. It goes back to a division of inheritance following the death of the last landgrave of all Hesse, Philip I in 1567.

The conflict began when the line of Hesse-Marburg died out in 1604. It escalated during Thirty Years' War. After a first settlement in the 1627 Hauptakkord, direct war between Hesse-Cassel and Hesse-Darmstadt broke out 1645 in the Hessian War proper. This open warfare began with the Siege of Marburg in 1645 and ended in April 1648 (but before the Treaty of Westphalia which was concluded later that year and ended the Thirty Years' War) with victory going to Hesse-Cassel. In the peace treaty, Hesse-Cassel received a quarter of Hesse-Marburg with the city of Marburg, while the rest remained with Hesse-Darmstadt.

During the Thirty Years' War, Calvinist Hesse-Cassel joined the alliance between Protestant Sweden and Catholic France, whilst despite its Lutheran beliefs, Hesse-Darmstadt, sided with the Emperor. In the course of the war, Hessian mercenaries fought both in the main Hessian lands as well as in Westphalia (Prince-Bishopric of Münster and Paderborn), in Upper Guelders, on the Lower Rhine (Electorate of Cologne), in the Duchy of Brunswick and other places.

This conflict should not be confused with the campaign by Landgrave Philip I of Hesse, supported by Prince-Elector John of Saxony against the two Franconian prince-bishoprics of Würzburg and Bamberg in 1528, which is also referred to as the "Hessian War".