Game concept
Bloc Supremacy War
The game also links it as Bloc Supremacy, Supremacy.
From the game's encyclopedia
A Bloc Supremacy War is a special type of War waged between the Leading Houses of two Sōryō House Blocs.
Unlike other Wars, all members of both Blocs will join.
The victorious Bloc will gain Cohesion, while the losing Bloc will lose a third of its Cohesion.
In addition, any Sōryō Member Houses of the losing Bloc whose House Head is not Loyal, Hooked by, a sub-Vassal of, an Ally of, Friends with, or Terrified of the losing Leading House's House Head, will join the victorious Bloc.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Bloc Supremacy War is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Bloc Supremacy War is a special type of War waged between the Leading Houses of two Sōryō House Blocs." It is part of House Bloc. The game also links it as Bloc Supremacy and Supremacy. Patch 1.20.1.2, from game/common/game_concepts/tgp_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/tgp_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.