You mentioned merc clans above. Here's an example:
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The Vlandians have 7 Vlandian clans. They have 7 merc clans employed plus 'Tulvo's Clan', which I assume is a rebellion clan. More than 1/2 their clans are not native Vlandian clans.
And thats part of the problem for those who face the oppoite of the op.
Constant hireing of mercs each time they get their noses bloodied instead of going for peace.
In my play, Vlandia decided to wage war on us(this was bit late game so Battania had 2 fiefs at that time left).
Rest was divided by Sturgia(us) and Vlandia.
We also had a few Western Empire castle in proximity to Vlandia.
I was around my holdings, Maruanth + Seonon, cause I "knew" Vlandia was going to attack. Since the 30 days peace was soon over, and most of our forces was travelling to frontlines of Khuzait - war is on.
Within very short time, they blitzed 3 castles from us(note theese had very low loyalty so they didnt put up much resistance tbh).
So naturally the ai being ai, it go peace with Khuzait, and then travel back to frontlines of war with Vlandia, meaning I'm now going to have to work overtime for 3-5 days before they arrive.
I summoned in a few lords to have a small army, and the started to defend the things they where no going for.
See heres the thing, soon as I started to bloody their nose, they hired mercs, instead of just "we got 3 castles" we got enough for this short war.
Instead they or my faction? not sure 0% intrest in peace.
So the mentioned 3 armies of our then came back to this side, and boom 3 castles back in our hands, boom the 2 castles of Battania they held + Car banseth in our hands.
When we sieged Sargoth Vlandia did want peace, and 3 of their lords had died in battle aswell.
But yah its fun in one sense, but its annoying in another as the only reason we got peace there was that Aserai also declare war on us, a war which goes nowhere tbh(since they never come to us, nor do ours to them(too far distance, and too much food needed to travel from a - b(consumption of food is way too heavy tbh for armies).
Dont get me wrong I had a period of the game where we after haveing had the inital war with Vlandia, which ended when they got rebuffed at the battle of Varcheg, and then the WE declared war upon them + Battania, we got peace.
Khuzait declared war on us, but the NE declared war next day on Khuzait, so peace.
Then it was peace for at the very least 1 ingame year before we had any action again at all.
Meanwhile the war vs those others raged on and on.
Ideally they change the "tribute system" to be tied to the 30 days grace period of peace to be max that, so they arent declaring war to pay less tribute.
And that once war is declare it should also last for min 30 days.
So you sort of avoid the issue of "peace all the time, that some seem to suffer from".
Lots of the mechanics seems good, but for some reason dont really pan that well out for some players, be it that some of us never get peace and others never get war.