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.