Prior to 1635, France provided indirect diplomatic and financial support to opponents of their Habsburg rivals in Spain and the Holy Roman Empire, but avoided direct involvement.

A key factor in European politics during the 17th century was the struggle between the Bourbon kings of France and their Habsburg rivals in Spain and the Holy Roman Empire.

This crisis moved Richelieu closer to direct intervention in the Thirty Years War; in October, French garrisons occupied towns in Alsace on the left bank of the Rhine, then part of the Empire.

To satisfy Richelieu's domestic critics, who questioned his alliances with Protestant powers, Sweden accepted the restoration of Catholicism in areas where it had been practised prior to 1618; France undertook to declare war on Spain, and both parties agreed not to make a separate peace.

[8] In addition to the treaty with the Swedes, France signed agreements with Bernard of Saxe-Weimar to provide 16,000 troops for a campaign in Alsace and the Rhineland, and an anti-Spain alliance with the Dutch.