Game concept
Debt
From the game's encyclopedia
Debt is the state of having a negative amount of GoldGold. This typically happens when a Ruler at war hires Mercenaries without having enough Gold to cover the full cost, or when they are at war for too long.
While in Debt you cannot declare new Wars, your Men-at-Arms do not reinforce, and your enemies will have an Advantage over you in battle. The deeper into debt you fall, the more penalties you will get — fewer Levies, reduced Popular Opinion, and your Vassals will like you less.
In addition to this, various other minor destabilizing events may occur, such as gaining County Corruption in your Domain Counties.
It is generally a good idea to strike your enemies while they are in Debt, as they will fight with reduced Advantage!
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.
Debt is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Debt is the state of having a negative amount of GoldGold." It is part of Gold. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
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.