What sorts of PoDs or changes would be necessary for the Dutch Revolt/Eighty Years War to result in the independence of a united Netherlands in the 16th or early 17th centuries? Moreover, what would the effects of such a maximally successful revolt be, both in the short-term and the long-term?
As far as "how" goes, my inclination as a decided non-expert is to think that several factors are necessary. First, the rebels need to be more militarily successful. Obviously, if the Spanish are not capable of effectively contesting their control over the Low Countries, then they are more likely to be able to win independence more quickly than occurred in OTL. Second, the religious conflict within the Low Countries needs to be suppressed, at least until after the war is over. Any united Netherlands at this time is clearly going to have a lot of Catholics and a lot of Calvinists, and there's no way to get there without having them fight together (as proven IOTL). Third, probably the Spanish need to be less competent. In some respects they were incompetent, obviously, in inflaming the revolt in the first place, but their military leaders seemed to be able enough, and Parma at least had the diplomatic skills to exploit (2) instead of just condemning Catholic and Calvinist alike to death.
I suppose the most obvious approach, to me anyway, would be to delay the start of the revolt somewhat, from the 1560s into the 1570s or even the 1580s. This might result in a stronger Calvinist position in the southern provinces, so making them more rebellious, and perhaps might rob Spain of some of its stronger leadership or lead them to become engaged elsewhere. If you combine this with a bit of luck on the part of the rebels, they might quickly overthrow royal government in the Low Countries and present Spain with a fait accompli; even if it decides to try to reconquer the place, it's at least plausible that the Dutch will be able to prevent it. But like I said, I am not an expert or especially knowledgeable in this subject.
As for longer-term effects, I have to imagine those would be large. The Dutch Republic exerted a lot of effort in trying to conquer the Austrian Netherlands IOTL, both because they were relatively wealthy and populated and because they had large fortification systems to provide buffers against the French. Here they just...have them from the beginning. This makes me suspect that they might be more adventurous in Europe, since they have a stronger position and don't need to worry so much about defending their southern flank. Overseas, they might also be more successful, given that they again have more men, more money, more ports, just more stuff going on. More enduring Dutch colonies in the Americas, or an even stronger Dutch presence in the Indian Ocean, Southeast Asia, and East Asia? Likewise, this will have major effects on England, which fought with and against the Dutch on a number of occasions in this period. The Dutch will, again, be stronger and richer, which will have effects on English politics and English decision-making. But again, I'm not an expert, so I'm not sure exactly how this will play out.
As far as "how" goes, my inclination as a decided non-expert is to think that several factors are necessary. First, the rebels need to be more militarily successful. Obviously, if the Spanish are not capable of effectively contesting their control over the Low Countries, then they are more likely to be able to win independence more quickly than occurred in OTL. Second, the religious conflict within the Low Countries needs to be suppressed, at least until after the war is over. Any united Netherlands at this time is clearly going to have a lot of Catholics and a lot of Calvinists, and there's no way to get there without having them fight together (as proven IOTL). Third, probably the Spanish need to be less competent. In some respects they were incompetent, obviously, in inflaming the revolt in the first place, but their military leaders seemed to be able enough, and Parma at least had the diplomatic skills to exploit (2) instead of just condemning Catholic and Calvinist alike to death.
I suppose the most obvious approach, to me anyway, would be to delay the start of the revolt somewhat, from the 1560s into the 1570s or even the 1580s. This might result in a stronger Calvinist position in the southern provinces, so making them more rebellious, and perhaps might rob Spain of some of its stronger leadership or lead them to become engaged elsewhere. If you combine this with a bit of luck on the part of the rebels, they might quickly overthrow royal government in the Low Countries and present Spain with a fait accompli; even if it decides to try to reconquer the place, it's at least plausible that the Dutch will be able to prevent it. But like I said, I am not an expert or especially knowledgeable in this subject.
As for longer-term effects, I have to imagine those would be large. The Dutch Republic exerted a lot of effort in trying to conquer the Austrian Netherlands IOTL, both because they were relatively wealthy and populated and because they had large fortification systems to provide buffers against the French. Here they just...have them from the beginning. This makes me suspect that they might be more adventurous in Europe, since they have a stronger position and don't need to worry so much about defending their southern flank. Overseas, they might also be more successful, given that they again have more men, more money, more ports, just more stuff going on. More enduring Dutch colonies in the Americas, or an even stronger Dutch presence in the Indian Ocean, Southeast Asia, and East Asia? Likewise, this will have major effects on England, which fought with and against the Dutch on a number of occasions in this period. The Dutch will, again, be stronger and richer, which will have effects on English politics and English decision-making. But again, I'm not an expert, so I'm not sure exactly how this will play out.