There is away around that issue..
First you create a sandbox tactical medieval game..with map builder.. a random map builder...plus all units nations and leaders etc etc..
You then create the Grand Strat game but do it at so it's bordering on operational (not sure if thats the right term for this sort of warfare). Anyway in this game you can either play out combat using a similar mechanic some of the indepth wargame use like WITE or you have an option that allows you if you own the tactical game to input your results be it through some sort of text file or it just asks you to input the result so I suppose you fill in an AAR..which could be shown at the end of the tactical battle...the Tactical wargame would be built in away you can state what terrain..the size of forces and troop types involved, weather, moral state experience etc etc..what leaders are involved..the type of engagement etc etc..and the game will then create the scenario for you to then battle against.
That way you've created two separate games but they can work in conjunction with each other...maybe it would be possible to merge them..but that might take an awful amount of coding genius. The tactical game would have been designed with the strategic game in mind..but still be a superb game in it's own right with historical scenarios and figures from history..and campaign etc.
You could even model actual castles and have them in the strategic game and also in the tactical game so when it comes to sieges in the tactical game the actual castle will be shown..I stick with either counters or some abstract method for troops rather than 3D rts style..as some battles would be huge..put all the effort into the gameplay..still make it look great but great for a 2D top down game.
ORIGINAL: The Gray Mouser
ORIGINAL: grogmaster
Its difficult to represent medieval warfare at a strategic level or operational level. But I think total war games did it quite well. But for hexes, no way. It just doesn't work that way. And Great Battles Medieval was a flop no matter how you suger-coat it.
As long as there was a suitably realistic and playble way of recruiting armies and keeping them in the field, then I dont see why it would be un-doable
Its my dream to see a game incorporate strategic, operational and tactical all the way thru

(premodern of course, no way you could do that for WW2) The problem is we would be asking for three games in one and many players would demand it be for the price of one...