I got this idea from reading about Owen Glendower (Owain Glyndŵr).
He made this proposal during his rebellion against Henry IV. He proposed that the northern earls - the Percys - form a northern English kingdom and the rival for the English throne Edmund Mortimer, form a southern English kingdom. Owen would then by the king of the newly formed Welsh kingdom. Henry IV would be overthrown.
The Owen Glendower wikipedia entry tells it better:
"Owain demonstrated his new status by negotiating the "Tripartite Indenture" with Edmund Mortimer and Henry Percy, Earl of Northumberland. The Indenture agreed to divide England and Wales among the three of them. Wales would extend as far as the rivers Severn and Mersey including most of Cheshire, Shropshire and Herefordshire. The Mortimer Lords of March would take all of southern and western England and the Percys would take the north of England. Although most historians have dismissed the terms of the Indenture as being highly ambitious and fanciful, R. R. Davies noted that certain internal features underscore the rootedness of Glyndŵr's political philosophy in Welsh mythology: in it, the three men invoke prophecy, and the boundaries of Wales are defined according to Merlinic literature."
So in game terms this would be a four-player game. Each player would have a track of local support that they would want to build and maintain by their actions. Other influence - for example, events in France, Ireland and Scotland - would be from a shared card deck. Each card would have four sections relating to each player. Each player would draw a card and could play the event on either themselves - to a lesser effect - or on another player at normal effect.
The objectives of the players are complex.
Henry IV only wins if he remains king of England and Wales. He gets a draw if he losses any portion of his kingdom, and an absolute loss if dethroned.
Edward Mortimer only wins if he becomes king of all of England; a draw if he is king of southern England; a loss if he gets nothing.
Owen only wins if he gets to be King of an independent Wales, a draw if he is some sort of overlord of Wales paying homage to another King and loss if nothing.
The Percys win if they get to be King of northern England, a loss if nothing else. They were not called Hotspur for nothing.