Why did Turenne make an alliance with Spain during the Fronde?

Turenne formed an alliance with Spain during the Fronde primarily as a result of his political opposition to Cardinal Mazarin and his association with the faction led by the Prince de Condé.

Following the arrest of Condé by Mazarin on January 18, 1650, Turenne fled to Stenay on the eastern border of Champagne. There, he joined forces with the Duchess de Longueville, Condé’s sister, and they formally entered into a treaty with the Spanish—who were then at war with France—to wage a rebellion against the government. This alliance was a strategic maneuver within the broader aristocratic uprising against the cardinal's authority. Turenne continued to fight alongside these rebel forces in Champagne until he was defeated at the Battle of Rethel in December 1650.1