A Total War Saga: TROY
Because on a vanilla campaign, it is very easy to be liked by everyone, to finish the campaign with lots of allies, hostile factions are destroyed by other factions and where factions accept the culture of others without worry.
With this mod, an intercultural penalty has been applied. Factions of the same culture will ally more easily with other factions of the same culture, since they will not like the other factions.
It will therefore be more difficult to cooperate with another culture. Everyone will defend their own culture or want to destroy a different one from ours.