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,
Henri de La Tour d'Auvergne, Viscount of Turenne for which many modern writers have blamed Turenne, appeared no more harsh a measure than the spirit of the times and the circumstances of the case permitted. The Peace of Westphalia (1648) brought little peace to France, which soon became involved in the civil war of the Fronde (1648–1653). Few of Turenne's actions caused sharper criticism than his adhesion to the party of revolt. The army of Weimar refused to follow its leader and he had to flee into the Spanish Netherlands, where he remained until the treaty of Rueil (March 1649) put an end to the first war of