The Dutch Revolt began in protest against the Spanish ruling monarch, Philip II. The Dutch throne had become one of the many hereditary seats of power that were amassed under the Habsburg Empire. When Charles V began the process of abdication, his son Philip II became king of Spain and ruler of the Dutch territories in 1556. Philip was born and raised in Spain, was only fluent in Spanish and was staunchly Catholic, so quickly instigated measures to curb Protestantism, which had become popular in the Netherlands following the spread of Calvinism. Protestant rebels in the northern provinces subsequently declared war against Spain and two opposing unions of Protestant and Spanish-controlled Catholic territories formed in the 1579 Unions of Utrecht and Arras. The twelve years’ truce, beginning in 1609, instigated a long period of economic warfare, which eventually concluded with the acceptance of official independence for the United Netherlands in the 1648 Peace of Münster.