In 1837, there had been negotiations between Spain and Belgium for a sale of Cuba. Britain opposed it because Belgium had its independence hardly recognized. But I imagine the following POD: suppose that in Spain Zumalacárregui, the Carlist general, survives and puts the Carlists in the Spanish throne and Isabel II fled to France. Carlist Spain accepts the sale of Cuba to Belgium, but this sale of Cuba does not happen in 1837 but ... in the early 1860s, while the Americans were too busy in their civil war to assert the Monroe doctrine. How would the Belgian administration manage the island? Cubans will surely revolt for their independence but how will Cuba's history unfold afterwards? I suppose that the Belgians will be more tender with the Cubans than they were with the Congolese, and that they will allow the use of the Spanish language, but only a short time later ...