Force peace rule:
Case 1: War between two nations.
If one side manages 99 warscore, the loser is at -3 stability and the war has been going on for at least 5 years, the winner can force peace with a stab-hitting peace offer.
Case 2: War between an alliance of 2 or more versus 1 nation (gang).
For any separate peace, see case 1.
If the alliance leader wants to force peace for the alliance against the 1 nation, he requires 99 alliance warscore and 99 warscore of his own (separately).
Case 3: War between 2 alliances of 2 or more nations.
For any non-alliance peace between two nations, see case 1.
For any alliance to separate nation peace deal (for any member of the other alliance, even leader), see case 2.
If the winning alliance's leader wants to force-peace the whole other alliance, he needs 99 warscore for his alliance on the other alliance and 99 warscore of his own against the losing alliance leader. It is the losing leader's stability that is taken into consideration.
Examples:
Alliance 1: FRA, BB
Allaince 2: HAB, ITA, SPA
FRA gets 99 ws on HAB while BB gets 10 ws on HAB. ITA and SPA have 0 warscore. Alliance 1 now has 99 ws on HAB and leader FRA has 99 ws. They can force-peace HAB when HAB gets -3 stab and after 5 years.
HAB is force-peaced.
Then ITA gets 50 ws on FRA and SPA gets 50 ws on FRA. Alliance 2 now has 99 ws on Alliance 1, but leader ITA only has 50 ws on leader FRA. They can not force-peace.
ITA now gets 99 ws on FRA and FRA gets 20 ws on SPA. Leader ITA can still not force-peace leader FRA for alliance, as Alliance 2 only has 79 ws on Alliance 1. But ITA can force-peace FRA separately, as they have 99 ws.
FRA is force-peaced separately, splitting the wars into: ITA vs BB and SPA vs FRA, BB.
Force-peace is now following cases 1 and 2.