There was a plot to overthrow Henry V (I think) which involved splitting England and Wales into three parts - Wales plus the English border, and England split in two. I think Glyndwr was one of the participants and Hotspur another. It was a pretty stupid idea even at the time and there's little evidence to suggest that the signants were even serious about the scheme, let alone that it would work, but I guess you could just say that it happens ITL...without a strong England it could happen, I guess...though I reckon that Wales just doesn't have the strength to maintain a consistent state of independence. Scotland would probably swoop to dismember the "upper England" and France would do something similar to the south, and at some point down the line Wales will become a tributary to France in some manner.