The struggle by the Netherlands for independence from Spain. The Low Countries formed part of the Spanish empire but the tactlessness of the Council of Regency for Philip II alienated the local nobles, who were excluded from government. High taxation, unemployment, and Calvinist fears of Catholic persecution aroused dangerous opposition which the Duke of Alba came to crush (1567) with a reign of terror and punitive taxation. Open revolt led by William I (the Silent) followed. He avoided pitched battles with the superior Spanish forces and exploited his local knowledge, saving besieged cities like Leiden (1573–74) by opening the dykes and flooding the countryside. The sack of Antwerp (1576) led to a temporary union of the whole Netherlands in the Pacification of Ghent. Calvinist excesses soon caused the southern provinces to form the Union of Arras (1579) and make peace with Spain. The northern provinces formed the Union of Utrecht and the war became a religious struggle for independence. William held out with foreign aid until assassinated (1584), when the leadership passed to Maurice of Nassau and the politician Oldenbarneveldt. The United Provinces were saved by Spain's commitment to wars against France, England, and Turkey. A truce (1609) was followed by recognition of full independence at the Peace of Westphalia (1648).