France openly entered the Thirty Years’ War against the Habsburgs in 1635. Its intervention transformed the conflict from primarily an internal German religious struggle into a wider European war involving the French and Spanish Habsburg powers.
France was governed by Louis XIII, with Cardinal Richelieu directing policy. Although Catholic, France viewed the Habsburgs as a strategic threat because their territories surrounded or pressed against French interests. Before direct intervention, Richelieu had supported the Habsburgs’ enemies through diplomacy, subsidies, and alliances, including assistance to Sweden and other anti-imperial forces.
After the Swedish defeat at Nördlingen in 1634, France became more directly involved. It declared war on Spain on 19 May 1635 and sent forces into the conflict. French troops fought both Spanish Habsburg forces and imperial forces linked to the Habsburg system. This is a classic example of political and strategic rivalry overriding religious alignment: Catholic France allied with Protestant Sweden against Catholic Habsburg opponents. France continued fighting until the settlements of 1648 and the later Franco-Spanish peace in 1659.