Apologies for bumping the thread!
But I'm actually quite keen for this for a timeline...
Cruising around Wikipedia and elsewhere, I've been researching the plausiblity of a Calvinist Commonwealth under Cromwell uniting England, Scotland, Ireland and [the Republic of] the Netherlands into one single political entity. It seems that for a plausible union to take place, there needs to be a readjustment in the political tensions between the Commonwealth and Republic and a greater focus on their similarities and intended goals.
Firstly, and most obviously, there was
militaristic partnership between England and the Netherlands against the territorial ambitions of the Hapsburgs which stretches all the way back to the Dutch revolt under Philip II of Spain. They'd fought together to beat the Spanish Armada and England had funded the Dutch in the Eighty Years' War with both finance and troops. However, with the seperate peace for the English in 1604, this was the first major schism between the two states (apart from their established economic rivalry enhanced by Holland's quick dominance over Iberian trade). Furthermore, there was also the rivalry established by the weakening of Portugal and Spain regarding territories overseas and colonies. Nevertheless, despite the huge
Dutch mercantile fleet they were outmatched by the
Commonwealth's superior navy. A combination of the two could have benefitted them greatly.
Most significantly, however, there was the inescapable truth that both the Commonwealth and the Dutch Republic were, as their names suggest, both republics and - very importantly - Protestant. As a result, when William II (of Orange) attempted to install military dictatorship,
the Dutch naturally sought their closest ideological allies for help.
This is the cusp point - it is now when the Dutch vaguely approach the English for union. If this move is clearer, perhaps with a stronger looking Orangist force, then Cromwell might be quicker to intervene with more definitive results. As you've all mentioned above, if William II stays alive, rather than dying of smallpox in 1650, and continues to threaten the Republic, I think a union is far more likely - perhaps even probable.
It was the death of William II that removed the urgency, and consequently I would his longevity as the first of several potential 'points of divergence.' Additionally, even if William does die in 1850, if the English delegation in the Hague is treated with greater skill and dexterity by the Dutch then it is possible that their differences could be put aside in the sake of union.
As Wietze says, William II not dying is a good PoD. The other way of doing it using him is even simpler, and doesn't need and Royal Princes killed off either;
PoD: 1650. William II of Orange cocks up his coup against Amsterdam and is reduced to camping miserably outside the walls of the city with his army. Things are patched over (and his death by smallpox is butterflied), while the Regents of Holland, increasingly pissed off with the Stadtholder, continue their secret negotiations with the Commonwealth. Finally, come 1652 or so, fighting erupts between the Orangists and their foes, and Oliver Cromwell, taking the Hollander promises of joining the Commonwealth very seriously, decides to take the New Model Army on an excursion...
There are other things, too, that may have averted the First Anglo-Dutch War (1652-1654) which naturally would have created a less-hositile relationship between GB and Holland.
The Hague was a hotbed of royalist support - Charles I's daughter Mary Henrietta Stuart, the Princess Royal, was a resident of the city, and pro-royalist English exiles had gathered there. Additionally,
the Dutch proposal of a free trade agreement (to counter English plans for world-dividing spheres of influence) was met with anger in the Commonwealth who saw it as a deliberate affront to their ambitions - when in fact it was merely a Dutchcentric compromise to avert war which resulted in the opposite. If you avert this reaction, war may be avoided.
In conclusion, then, it seems that the
Anglo-Dutch Union of 1650 could - quite easily in my opinion - be formed in the midst of
anti-monarchist ambition, religious similarity and a considerable military and economic base. I think I'd help if William II survived, or (if he did die) was replaced by just as strong a force to spook the Netherlands enough to seriously seek help, rather than the tentative inklings that they put forward in OTL. Such a union would, undoubtedly, form one of the most significant geopolitical players of the world at the time, and form a considerable threat to the monarchies of the continent - assuming Cromwell doesn't go rogue, of course. I can see it potentially linking up with the Protestant movements (as religious differences will be MUCH more significant internationally in this world) in the various Germanies and Scandinavia. I have visions of an Anglo-Dutch Commonwealth, Scandinavia and *German* alliance against the Catholic powers of Spain, France(?) and Austria, in particular.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
OK - that's the seminar over.
Please, somebody, correct or embellish some points as you see fit. It'd be useful now that I'm seriously considering this as the foundation for a timeline.