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,
Treaty of the Pyrenees Spanish Habsburg victories in the Dutch Revolt in the 1620s and at the Battle of Nördlingen against Sweden in 1634. By 1640, France began to interfere in Spanish politics, aiding the revolt in Catalonia, while Spain responded by aiding the Fronde revolt in France in 1648. During the negotiations for the Peace of Westphalia in 1648, France gained the Sundgau and cut off Spanish access to the Netherlands from Austria, leading to open warfare between the French and Spanish. After 23 years of war, an Anglo-French alliance was victorious at the Battle of the Dunes in June 14, 1658, but