Sensible Expansion

This mod aims to make borders created through AI (and player, if you so choose) conquest and expansion cleaner and more visually appealing, in addition to prevent larger realms from snowballing and excessively blobbing.

It achieves this by increasing CB costs for “undesirable” wars, forcing realms to prioritize local targets first, and thus hopefully results in a better borders. The changes are applied through top-level multipliers rather than modifying individual CBs, therefore pretty compatible with mods that adds new CBs.

Below are the features and conditions that increase CB costs:

(Localized: "Relative Realm Size")
Applies a scaling multiplier for every 10 realm size above the defender, if the attacker is sufficiently larger than the defender, and either:
a. The attacker is of Empire tier or higher, OR
b. The defender does not control any counties within the attacker’s de jure territory.

Example:
In the 867 start, the King of France will incur increased CB costs when targeting the Asatru Count in León (within the Kingdom of Brittany), but normal costs against Haesteinn (within the Kingdom of Aquitaine, which is controlled by the King of France).

(Localized: "Costly Venture")
Applies a 10× multiplier if ALL of the following are true:
a. The attacker is an administrative realm.
b. The attacker does not control all of its de jure counties.
c. The defender does not control any counties within the attacker’s de jure territory.

Example:
In the 876 start, the Byzantines will incur a massive increase in CB costs if they attempt to conquer Crimea, but normal costs within the Balkans.

(Localized: "Unsecured Heartlands")
Applies a 10× multiplier if ALL of the following are true:
a. The attacker is landed.
b. The attacker is a Duke or higher, and the title is NOT titular, landless, or a family title.
c. The attacker does not control all of its de jure counties.
d. The defender does not control any counties within the attacker’s de jure territory.

Example:
In the 867 start, the King of Brittany will incur increased CB costs against any ruler except the Asatru Count of León, since León is part of de jure Brittany and the king does not yet fully control it.

Normally, Conquerors ignore CB costs. This mod changes that so Conquerors only ignore costs if either:
a. The attacker completely controls the de jure Empire of their capital county.
b. The defender controls at least one county within the de jure Empire of the attacker’s capital county.

Example:
In the 867 start, if a Conqueror spawns in the Duchy of Bohemia (Duke Neklan), their capital is in Praha (within the Empire of West Slavia). They will have no CB cost against rulers within de jure West Slavia, but normal costs (including the modifiers above) when targeting rulers in Germania.

— —
The cost multiplier may seem exorbitant, but CB costs are pretty small to begin with, and war targeting territories protected by the increased cost above may still happen. To test this, you can play the observer mode with 100% Increase on Conquerors game rule. Currently, the increased conquest cost only affects the AI by default, but you can change this through a game rule to make it apply to both the player and the AI.

Suggestions to improve the mod towards the intended purpose above is welcomed. Suggestions for improving the code—whether for performance or overall quality—would be greatly appreciated.

– Added a game rule to control whether the increased conquest cost affects only the AI or both the player and AI.

This mod edit the common_cb_cost_multiplier_core in commonscript_values99_casus_belli_values.txt. Therefore, any mod that also modify the same variable might not work correctly with this mod.