Game concept · All Under Heaven
Mandala
The game also links it as Mandala Government, Mandalas.
From the game's encyclopedia
Under the Mandala Government Form, the Domain Limit and amount of Direct Vassals are limited. Instead the Liege and Suzerain are reliant on Tributaries for expanding their realm.
A Mandala Ruler can aspire to be seen as a God King, or Devaraja, and then relies on Mandala Radiance to acquire and keep Tributaries.
A Ruler must maintain Opinion and grow relations with their Tributaries to keep them long-term. On succession Tributaries may scatter unless the Ruler is a worthy Devaraja Successor.
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.
Mandala is an entry of Crusader Kings III's in-game encyclopedia (All Under Heaven). The game explains it: "Under the Mandala Government Form, the Domain Limit and amount of Direct Vassals are limited." The game also links it as Mandala Government and Mandalas. 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.