How about manpower limits for all kingdoms - meaning they can't have more units at any one time than their current manpower.

Make the limit usually equal total to level of all provinces - but the level of the capital province is say doubled or trebled for working out manpower, so small kingdoms can still have an army.

(Also some of the smallest kingdoms - e.g Dragonhold just need to start with more provinces - two provinces is not enough - give them a couple more taken from Iron Barony and/or Vessoi)

Then you'd have manpower varying according to race and terrain.

So e.g elves would only get manpower from forest hexes, would get half manpower level rounded up from hills provinces, no manpower from other provinces.

Dwarves and giants would get normal manpower from mountain or hill provinces. None from other provinces.

Orcs would get double manpower from mountain or wasteland provinces, normal from others.

Humans get manpower from all province types - and double from plains with a river valley going through them.

Undead would be exempt from manpower - the manpower limits just wouldn't apply to them.

Each time a unit is destroyed your kingdom's manpower is reduced by 1 - and that 1 manpower takes a year to get back . Or for dwarves and elves you never get it back, or it takes 5 or 10 years (to represent them being races with less numbers and longer lifespans, less children etc).

Some units - goblins, orc grunts etc could require only half a manpower point to raise - and you'd only lose half a manpower if they were killed.

There could be some buildings (and maybe spells too) that increased manpower.

Some units that represent single individuals (dragons, generals etc) could cost zero manpower to raise.

This would lead to fewer, but more important battles - and add more variety and atmosphere, as playing as different races would now be more different.

While i love playing Sonneneve it seems wrong that i can recruit unlimited hordes of elves. That should be something only humans , orcs or undead can do imo, with dwarves and elves being limited in number and unable to make up heavy casualties.