 At the same time, the Muslim Barbary corsairs, acting under the general authority and supervision of the sultan, regularly devastated the Spanish and Italian coasts, crippling Spanish trade and chipping at the foundations of Habsburg power.In 1536 Francis I of France allied himself with Suleiman against Charles.While Francis was persuaded to sign a peace treaty in 1538, he again allied himself with the Ottomans in 1542 in a Franco-Ottoman alliance.