William responded by leading a large army into
Brabant, but Alba carefully avoided a confrontation, expecting the army to fall apart quickly. He proved to be right, as William lacked the money to support the army. William made several more plans to invade in the next few years, but little came of it, lacking support and money. He remained popular with the public, partially through an extensive
propaganda campaign through pamphlets. One of his most important claims, with which he attempted to justify his actions, was that he was not fighting the rightful owner of the land, the Spanish king, but only the inadequate rule of the foreign governors in the Netherlands, and the presence of foreign soldiers. On
April 1, 1572 a band of Watergeuzen captured the city of
Brielle, which had been left unattended by the Spanish garrison. Contrary to their normal "hit and run" tactics, they occupied the town and claimed it for the prince. This event was followed by other cities in opening their gates for the Watergeuzen, and soon most cities in
Holland and
Zeeland were in the hands of the rebels, notable exceptions being
Amsterdam and
Middelburg. The rebel cities then called a meeting of the
Staten Generaal (which they were technically unqualified to do), and reinstated William as the stadtholder of Holland and Zeeland.
Concurrently, rebel armies captured cities throughout the entire country, from
Deventer to
Mons. William himself then advanced with his own army and marched into several cities in the south, including
Roermond and
Leuven. William had counted on intervention from the French Protestants (
Huguenots) as well, but this plan was thwarted after the
St. Bartholomew's Day Massacre on
24 August, which signalled the start of a wave of violence against the Huguenots. After a successful Spanish attack on his army, William had to flee and he retreated to
Enkhuizen, in Holland. The Spanish then organised countermeasures, and sacked several rebel cities, sometimes massacring their inhabitants, such as in
Mechelen or
Zutphen. They had more trouble with the cities in Holland, where they
took Haarlem after seven months and a loss of 8,000 soldiers, and they had to give up their
siege of
Alkmaar.
In 1574, William's armies won several minor battles, including several naval encounters. The Spanish, now lead by Don
Luis de Zúñiga y Requesens who succeeded Alba in 1573, also had their successes, and their decisive victory in the
Battle of Mookerheyde in the south east, on the
Meuse embankment, on
14 April cost the lives of two of William's brothers, Louis and Henry. Requesens's armies also besieged the city of
Leiden. They broke up their siege when nearby dykes were cut by the Dutch. William was very content with the victory, and established the
University of Leiden, the first university in the Northern Provinces. William married for the third time on
24 April 1575. He had his previous marriage legally disbanded in 1571, on claims of insanity of his wife Anna.
Charlotte de Bourbon-Monpensier, a former French
nun, was also popular with the public. Together, they had six daughters.
After failed peace negotiations in
Breda in 1575, the war lingered on. The situation improved for the rebels when Don Requesens died unexpectedly in March 1576, and a large group of Spanish soldiers, not having received their salary in months, mutinied in November of that year and
unleashed the Spanish Fury on the city of Antwerp, a tremendous propaganda coup for the
Dutch Revolt. While the new governor,
Don John of Austria, was under way, William of Orange managed to have most of the provinces and cities sign the
Pacification of Ghent, in which they declared to fight for the expulsion of Spanish troops together. However, he failed to achieve unity in matters of religion. Catholic cities and provinces would not allow freedom for Calvinists, and vice versa.
When Don John signed the
Perpetual Edict in February 1577, promising to comply with the conditions of the Pacification of Ghent, it seemed that the war had been decided in favour of the rebels. However, after Don John took the city of
Namur in 1577, the uprising spread throughout the entire Netherlands. Don John attempted to negotiate peace, but the prince intentionally let the negotiations fail. On
24 September 1577, he made his triumphal entry in the capital Brussels. At the same time, Calvinist rebels grew more radical, and attempted to forbid Catholicism in their areas of control. William was opposed to this both for personal and political reasons. He desired freedom of religion, and he also needed the support of the less radical Protestants and Catholics to reach his political goals. On
6 January 1579, several southern provinces, unhappy with William's radical following, sealed the
Treaty of Arras, in which they agreed to accept their governor,
Alessandro Farnese, Duke of Parma (who had succeeded Don John).
Five northern provinces, later followed by most cities in Brabant and
Flanders, then signed the
Union of Utrecht on
23 January, confirming their unity. William was initially opposed to the Union, as he still hoped to unite all provinces. Nevertheless, he formally gave his support on
3 May. The Union of Utrecht would later become a
de facto constitution, and would remain the only formal connection between the Dutch provinces until 1795.