William the Silent
Declaration of Independence

In spite of the renewed union, the Duke of Parma was successful in reconquering most of the southern part of the Netherlands. Because he had agreed to remove the Spanish troops from the provinces under the Treaty of Arras, and because Philip II needed them elsewhere subsequently, the Duke of Parma was unable to advance any further until the end of 1581.

In March 1580 Philip issued a royal ban of outlawry against the Prince of Orange, promising a reward of 25,000 crowns to any man who would succeed in killing him. William responded with his Apology, a document (in fact written by Villiers) in which his course of actions was defended, the person of the Spanish king viciously attacked, and his own Protestant allegiance restated.

In the meantime, William and his supporters were looking for foreign support. The prince had already sought French assistance on several occasions, and this time he managed to gain the support of Francis, Duke of Anjou, brother of King Henry III of France. On 29 September 1580, the Staten Generaal (with the exception of Zeeland and Holland) signed the Treaty of Plessis-les-Tours with the Duke of Anjou. The Duke would gain the title "Protector of the Liberty of the Netherlands" and become the new sovereign. This, however, required that the Staten Generaal and William renounce their formal support of the King of Spain, which they had maintained officially up to that moment.

On 22 July 1581, the Staten Generaal declared that they no longer recognised Philip II of Spain as their ruler, in the Act of Abjuration. This formal declaration of independence enabled the Duke of Anjou to come to the aid of the resisters. He did not arrive until 10 February 1582, when he was officially welcomed by William in Flushing. On 18 March, the Spaniard Juan de Jáuregui attempted to assassinate William in Antwerp. Although William suffered severe injuries, he survived thanks to the care of his wife Charlotte and his sister Mary. While William slowly recovered, Charlotte became exhausted from providing intensive care and died on 5 May. The Duke of Anjou was not very popular with the population. The provinces of Zeeland and Holland refused to recognise him as their sovereign, and William was widely criticised for what was called his "French politics". When Anjou's French troops arrived in late 1582, William's plan seemed to pay off, as even the Duke of Parma feared that the Dutch would now gain the upper hand.

However, Anjou himself was displeased with his limited powers and secretly decided to seize Antwerp by force. The citizens, who had been warned in time, ambushed Anjou and his troops as they entered the city on 18 January 1583,in what is known as the " French Fury ". Almost all of Anjou's men were killed, and he was reprimanded by both Catherine de Medici and Elizabeth I of England (whom he had courted). Anjou's position became untenable, and he subsequently left the country in June. His departure discredited William, who nevertheless maintained his support for Anjou. William stood virtually alone on this issue and became politically isolated. Holland and Zeeland nevertheless maintained him as their stadtholder and attempted to declare him count of Holland and Zeeland, thus making him the official sovereign. In the middle of all this, William married for the fourth and final time on 12 April 1583 to Louise de Coligny, a widowed French Huguenot and daughter of Gaspard de Coligny. She was to be the mother of Frederick Henry (1584–1647), William's fourth legitimate son. With her, "Father William", as he was affectionately styled, settled at the Prinsenhof at Delft, and lived like a simple Dutch burgher.
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