Hey, I'm Dutch myself and there is something I don't get. Since the 1560s, the Dutch revolted against the Spanish rulers under the leadership of stadhouder William of Orange-Nassau (William the Silent). In 1581, the Dutch Staten-Generaal declared itself an independent country using the Act of Abjuration (Plakkaat van Verlaetinghe). They tried to find a new monarch, in Francis (Duke of Anjou) or Robert Dudley of Leicester.
The point I don't get: why not install William the Silent as monarch, if you're looking for someone in 1580?
Some years ago, I asked my history teacher in school. He said William was killed. That is true, but that took place in 1584, three years after the Act of Abjuration.
Thanks a lot for helping me!
Basically, because foreign leaders opened up foreign alliances.
Remember that the Dutch revolt is called the 80 Years' War for a reason: on 1580, though the States General felt strong enough to declare independence from Spain, the revolution's success was not yet guaranteed. The Dutch needed foreign support to secure themselves, and an easy way of getting that was through a foreign ruler.
As the son of Henri II and brother to Francis II, the Duke of Anjou represented the possibility of a French alliance, with all the extra manpower and resources that entailed. After the French plan failed in 1583, William started consolidating power; he was offered the countship in 1584, but was killed before negotiations went anywhere.
When William the Silent died, Maurice of Nassau was only sixteen years old and not yet trusted with the same power as his father. He was not offered the countship, and so a void still existed at the top of the Dutch government. At first, the overlordship of the Netherlands was offered to Henry III of France, for pretty much the same reasons it was offered to Anjou. But Henry was dealing with the French Wars of Religion at the time, and he would have had to guarantee the Calvinist religion in the Netherlands had he accepted -- so it was politically out of the question. The next choice was England; Elizabeth didn't want to get tangled up with the Dutch question, but she didn't want to see a total victory on Spain's part either, so that's where Dudley comes in as the leader of an English expeditionary force and Governor-general of the Netherlands. As Elizabeth would later make very clear, she expected Dudley to be Governor-general on the States' behalf, not hers, so the plan backfired a bit there.
The search for a foreigner to rule the Dutch stopped after Dudley primarily because of because Johan van Oldenbarnevelt, who consolidated the leadership of the government into a single role filled by a native Dutchman. Of course, that only ended the internal debate; Henry IV of France was still intermittently interested in taking personal leadership of the Netherlands, even if the Dutch themselves were no longer too keen on the idea.
The major source I used for this was Herbert H. Rowen's The Princes of Orange: The Stadholders in the Dutch Republic (Cabridge University Press, 1988), which is a really good institutional history of the Stadhouderate.
The reason was that William of Orange didn't want to be head of state. They have urged him to do so but he didn't want the King of Spain give any reason to declare that he did lead the revolt just for himself. For personal gain so to speak.