Hessian War died out, and peaked after 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 aftermath, Upper Hesse was divided and parts of its territory went to the now stronger Hesse-Cassel. At a European level the Hessian War must be viewed in the larger context of the Thirty Years' War, in which the reformed Hesse-Cassel sided with the Protestant Swedish party, whilst Hesse-Darmstadt,
Peace of Münster for approval; it was ratified by the Spanish and Dutch delegations on 15 May, with the States General narrowly approving the Treaty on 5 June 1648. The Peace of Münster together with the Treaty of Münster between the Holy Roman Emperor, France and their allies and the Treaty of Osnabrück involving the Holy Roman Empire, Sweden and their allies were collectively known as the Peace of Westphalia. While European conflict continued, this marks a significant point in the transition to sovereignty based on states rather than individuals e.g. the Hapsburgs. Sovereignty has been defined by historian Harry Hinsley as "the