In 1568, during the reign of Philip II of Spain, the Netherlands, until then under the rule of the Spanish Empire, took up arms against the Spanish crown. The first phase of the war began with two unsuccessful invasions of the provinces by mercenary armies under Prince William I of Orange (1568 and 1572) and foreign-based raids by the Geuzen or Sea Beggars, (irregular Dutch land and sea forces). By the end of 1573 the Beggars had captured the bulk of the provinces of Holland and Zeeland as well as converted the populace to Calvinism, and secured against Spanish attack. The other provinces joined in the revolt in 1576, and a general union was formed.