Game concept
Ancestral Claim
From the game's encyclopedia
The Ancestral Claim Casus Belli allows you to annex all lands within a title with which you have a claim gained through a Legitimizing Legend.
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.
Ancestral Claim is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "The Ancestral Claim Casus Belli allows you to annex all lands within a title with which you have a claim gained through a Legitimizing Legend." Patch 1.20.1.2, from game/common/game_concepts/06_ce1_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/06_ce1_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.