The fact that his wife was only the fifth daughter of Frederick Henry, and that they were married after the death of her father, would later take on a special significance in the quarrel about the inheritance of the title of Prince of Orange after the death of William III of England in 1702. This was because Frederick Henry had made a provision in his will that if his male line would die out the title of Prince of Orange would be inherited by the male issue of the line of his elder daughter Louise Henriette of Nassau. This might even have been the case without this provision, had William III not himself left the inheritance to the descendants of William Frederick in his will. The inheritance therefore came down to a clash of testaments, with the outcome that both claimants eventually took the title and divided the material inheritance. William Frederick was a paternal grandson of John VI, Count of Nassau-Dillenburg, a younger brother of his wife's paternal grandfather William the Silent. When John died in 1606 his inheritance was divided among his five sons, one of which was William Frederick's father Ernest Casimir, who received the title of Count of Nassau-Dietz and followed his eldest brother William Louis, Count of Nassau-Dillenburg as Stadtholder of Friesland, Groningen and Drenthe in 1620. William Frederick inherited the Nassau-Dietz possessions, the county of Diez and the county of Spiegelberg from his elder brother Henry Casimir I of Nassau-Dietz, who died childless in 1640.
Career
As a second son, William Frederick did not seem destined for the career he eventually would follow. He studied at Leiden University and the University of Groningen and subsequently took a commission in the army of the Dutch Republic, like his male ancestors and his brother. As such he was a junior partner of his future father in law and brother in lawWilliam II, Prince of Orange. However, his elder brother died in action near Hulst in 1640. As Henry Casimir was unmarried, and did not have children, William Frederick inherited his titles. However, as the office of stadtholder was not yet hereditary, William Frederick only managed to be appointed in Friesland. The stadtholdership in Groningen and Drenthe went to Frederick Henry, not without a struggle with William Frederick, however. After Frederick Henry's death in 1647 William II succeeded his father also in these two provinces as stadtholder. Only when William II died in 1650, just a week before his son William III was born, did William Frederick obtain the stadtholdership in the other two provinces also. At that time he might have obtained the stadtholdership in the five other provinces also. After all, the stadtholderate was an appointive office. The elder branch of the Nassau family might have "first claim" to the office, but as the "claimant" was a newborn babe, such a claim was not to be taken seriously. Yet, to avoid a quarrel with the members of that elder branch William Frederick did not press his personal claim, but offered to serve as lieutenant-stadtholder in the five provinces until the infant William III would come of age. He might have been taken up on that offer, except for the events that preceded the death of William II. William had performed a military coup d'état against the States of Holland in the course of a quarrel about military policy. William Frederick had played a key role in that coup by leading the attempt to seize the city of Amsterdam by force in August, 1650. Though the attempted seizure was unsuccessful, the coup had not been. However, after William's death the Holland Regents seized their chance to revert to the status quo ante. They decided to leave the stadtholdership vacant in their province, followed by the four other provinces in which William had been stadtholder, thus inaugurating the First Stadtholderless Period. Because of his role in the coup William Frederick was politically unacceptable, not just as a stand-in for William III, but also on his own account. The office of stadtholder was a provincial office. On the federal level William II had fulfilled the office of Captain general of the Union, like his father and uncle before him. William Frederick again would normally have been in line for this office, except for the same political awkwardness that blocked his appointment to stadtholder in Holland. Again he offered himself as lieutenant-captain-general, but again the Regents decided to leave the function vacant. William Frederick did not even get the function of acting commander-in-chief, which went to a noble from Holland. This was to be the story of William Frederick's life. He tried to act as the de facto head of the Orangist party, in opposition to the States Party faction of Grand PensionaryJohan de Witt and his uncle Cornelis de Graeff, but was usually outwitted and checked by De Witt at every step. The fact that the members of the senior branch of the family were suspicious of his ambitions made his position even more difficult, even after he married into that senior branch. Nevertheless, outside the Netherlands those ambitions met with more success. In 1654 his title of Count was "upgraded" to Imperial Prince by the Holy Roman Emperor. Within the Empire this provided him with more prestige, which however did not translate to more prestige in the Republic. For a while, in the late 1650s, there seemed to be a chance of becoming Commander-in-chief, as part of a political compromise, brought together by De Witt, but nothing came of it. Only during the campaign against Bernhard von Galen during the Münster occupation of East Friesland, was he entrusted with a command in the field. He was successful in the reconquest of a strategic fortress, but shortly afterward he died on 31 October 1664 in an accident with a pistol that fired unexpectedly. Before his death he had persuaded the States of Friesland that his son Henry Casimir II should succeed him as stadtholder. The States kept their word, accepting a "regency" of the young boy's mother. The Frisian stadtholderate was made hereditary in 1675.
