Noticed the same problem. Going to add my ideas:
1) If a kingdom is already at war with 2 or more kingdoms, then they shouldn't declare war on another kingdom.
2) If a kingdom has fewer than 5 clans and is already at war with at least 1 kingdom, then they shouldn't declare a new war.
3) Kingdoms should only declare war on neighboring kingdoms. (If they have settlements right next to each-other.)
Thanks for the response, I kind of figured I wouldn't be alone but thank you for responding
Regarding your ideas I think we agree on something needs to change but I don't know if I'm completely sold on wanting exactly what you are as a resolution.
1 I agree with this mostly, I think 2 may be a bit too restrictive, but I agree with the sentiment 100%
2 I think available members is a better measure as 5 factions of 6-8 members can be more than a faction of 7 4-5s, but again agree with sentiment
3 I kind of agree, I'd like to see it heavily weighted that they won't seek to engage in a long ranged war, however, let's say you attacked a village, then the Lord that came to defend it, then you captured and executed them, I don't want the AI to say nah that's cool because there's a kingdom between us.
I think we definitely agree on direction though