What if in an alternate timeline, The Netherlands kept Belgium because there is no Belgian Revolution in 1830. I think that in this case, it is reasonable to assume that World War One would still happen: Franz Ferdinand is still killed in 1914 and the Great Powers like Germany, France and Russia still go to war.
But how would this war look like? What role would a still alive United Kingdom of the Netherlands play in it? And what would be the other differences?
Thoughts?
I am not sure if the Netherlands keeping Belgium ensures enough butterflies that still leads to WW1.
But for the sake of it...
The Dutch were pretty pro-German, especially with the Boer Wars the British had started. They may be convinced by the Germans to pass the German troops from the North although even with Belgium, the Dutch would be a constitutional monarchy with the parliament leading the country. So they may not be urged to let Germany pass and draw the ire of the British against Dutch Ship.
But...! The Germans can just hold their ground in the Elzas while the French lose many men. If the French do something like trying to move through the Ardennes against Germans, the Germans have legal grounds to enter the area that would have been Belgium and with the Dutch fighting along with them.
Considering how close France was at a mutiny in 1917 in OTL, there is a good chance France will lose this, with or without British aid.