Figured I'd bump this. I was just trying to consider some possible POD's for the English Civil War. Possibly as a way to suppress it. Now I not well versed in English history, for reasons most of you can probably guess, but I've recently started to peak at bits, and its usually pretty enjoyable learning, so I figured I'd take a crack at the Civil War period, which has always been a good dig site for TL's.
So the question, perhaps framed differently, is what if Buckingham had won at Cadiz? If he had come back from Cadiz a hero, then could Buckingham have not been as much hot water if he still fails at La Rochelle (if there even is a La Rochelle ITTL's 1627), giving Charles no need to dismiss parliament and establish his era of personal rule? At least thats what I've got, obviously, this is not my strong point, and Cadiz could obviously have more immediate repercussions in Europe itself, including Spain's possible response to such an attack and what would happen to Cadiz. Because I don't see the Spanish letting go of Cadiz, so that would probably be a few sieges away from falling anyhow.