Under what circumstances could a Hohenzollern King rule on the Dutch throne between 1800 - 1914?
Depending on your PoD, how does it effect German unification,
Depending on your PoD, how does it effect German unification,
The thirty year war is both too late for that and too early. Too late, because at that point the trappings of the republic were already made, so the Netherlands would not want a king anymore, not did it need a protector (besides that France was an ally durung the thirty year war). Too early since at that point Brandenburg was not important or strong enough yet to become a protector of the Netherlands.The Great Elector of Brandenburg Prussia spent his exile in The Netherlands during the Thirty Years War, which is the reason why the family converted to Calvinism. It's not unreasonable to imagine a timeline where he is offered the crown of the Netherlands IMHO, most likely if France annexes Belgium/the Spanish Netherlands, prompting the Dutch to want a reasonably strong protector.