Prelude
By 1576 the Habsburg Netherlands had been embroiled in a civil war for a decade already, during which Calvinist rebel forces had captured most of Holland and Zeeland (with the notable exception of Amsterdam) but had seen little success in the remainder of the region. There had been two Governor-Generals during this period, first the hard-handed and direct Duke of Alba from 1567 to 1573, and then the more diplomatic Luis de Requesens from 1573 to 1576. By the end of 1575 de Requesens was a fairly successful and well-liked governor, most notably having crushed an invasion by the brothers of William of Orange (the rebels' leader) at the Battle of Mookerheide. However, in September 1575 Philip II had to default on his debts and the crown's payments for troops in the Netherlands ceased, and this then forced the governor to end his campaigns. Over the following year chaos erupted as the royal troops began to mutiny. Requesens then died in March 1576, which marked the beginning of an 8-month long period without a governor-general in the Netherlands.
In fact, the king had already appointed his half-brother Don Juan as governor-general soon after the death of Requesens, but rather than going to the Netherlands as his brother's instructions told him to Don Juan instead went straight to the Spanish court in Madrid to question his brother. The issue was that Don Juan, a rather ambitious and impatient figure, was at that moment in time part of a conspiracy that would have overthrown queen Elizabeth of England and have installed him as king alongside Mary Stuart, and he was most displeased with the news that these plans would have to be delayed and that he was instead going to be sent to the Netherlands. After several months of arguing and demanding guarantees Don Juan finally left for the Netherlands, where he arrived on the 3rd of November.
In the meantime the situation in the Netherlands had further deteriorated. By now several provinces had raised their own armies to fight the increasingly dangerous mutineers. A bloodless coup had overthrown the Council of State, and soon thereafter the States-General had convened without royal authorization to take over the day-to-day governance. And nearly every single province had sent representatives to Ghent for peace negotiations with William of Orange, which would ultimately result in the Pacification of Ghent. The Pacification consisted of 25 clauses, of which some of the most important ones were general amnesty for the rebels, the return of all properties seized by the Duke of Alba’s “blood court”, the expulsion of all foreign soldiers, and the temporary end of persecution of heretics until a permanent settlement was made in the States-General.
Don Juan arrived too late to prevent the Sack of Antwerp by the mutineers, which begun the day after his arrival (when he was in Luxembourg) and lasted 3 days. Soon thereafter he was presented with the terms of the Pacification of Ghent by envoys of the States-General, who informed him that they would only formally recognise him if he confirmed these and saw to it that they would be fulfilled. He refused on the grounds that they had been drafted without the input of a royal representative and because he feared they meant the Catholic church would no longer be recognised as the supreme church. Only in December, under the mediation of Philip III de Croy (the Duke of Aarschot) and Gerard van Groesbeek (the Prince-Bishop of Liege), and with the reassurance of several professors from the University of Leuven that the Pacification did not inherently threaten the position of the Catholic church, did Don Juan finally open up. And even then only with a renegotiated set of terms.
This resulted in the Perpetual Edict of 1577, also known as the Peace of Marche-en-Famenne, which upheld just about every clause of the Pacification but noticeably differed from it by explicitly recognising the Catholic church as the supreme church in all the Netherlands. Because of this Willian of Orange would refuse to recognise the edict. Don Juan then finally crossed the border of Luxembourg for the first time. In early March he made his first "Joyous Entry" at Leuven, he sent envoys to Antwerp who began to organise the departure of the foreign troops (except the Germans, who were mercenaries that would not leave before being paid), and also to Dordrecht to negotiate with the Prince of Orange (but this would fail).
By the end of April all foreign troops had crossed the border and on the 1st of May Don Juan finally made his entrance into Brussels to be formally recognised as Governor-General. His stay in Brussels was short-lived however because he constantly felt the presence and pressure of the Organists through civil unrest in the city and implicit opposition from the local elite. On the 5th of June he abruptly left Brussels for Mechelen, in part out of fear for the Organist elements in Brussels, but also to negotiate with the German mercenary captains about their payment, and to begin enforcing the religious terms of the Perpetual Edict. Here he made the fatal mistake of getting personally involved in the persecution of protestants, rather than leaving the local institutions to it. Although he technically, legally was allowed to do so it was still a poor image and a bridge too far for some...
Historically this was the point where Don Juan began to receive increasingly more urgent warnings from some of his allies, most importantly the Duke of Aarschot, that he had to leave Mechelen. But in this timeline he is killed before he gets the chance to do so.
We now know that Don Juan had personally given up all hope for a peaceful conclusion by this point, and in his private correspondence with Philip II he was already urging the king to send back his armies from Italy. Later that same July he would take matters into his own hands and with a handful of loyal nobles and his personal guard he would take control of the citadel of Namur, in violation of the Perpetual Edict. A few months later his brother gave in, and along with the Italian tercios came a new figure to the Dutch stage: Alexander Farnese (another relative of the king), who would prove to be one of the most important figures for the Habsburg war efforts in the Netherlands. But none of this would now get to materialise as it did iotl.
