Game concept

Mercenary Contract

The game also links it as Mercenary Contracts.

From the game's encyclopedia

Establishing a Mercenary Contract incurs a one-time cost which allows the use of their troops for 36 months.

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.

Mercenary Contract is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Establishing a Mercenary Contract incurs a one-time cost which allows the use of their troops for 36 months." The game also links it as Mercenary Contracts. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.

for a guide, post or blog

Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.