Mod concept: What if annexing territories had a manpower requirement for nations that are regional powers or higher?
The point of this concept is to make it so that larger powers, while they would generally hold the advantage, would be less prone to snowballing than other factions would be. As you guessed from the title, this is accomplished by making manpower a key resource in being able to actually annex the territory. This will also hopefully wind up making it so that the AI is less prone to just annexing nations into extinction, making for more interesting gameplay.
This is both historically accurate and makes sense for the gameplay, now I will let you imagine how this concept will work depending on how big a faction is.
LANDLESS RABBLE/MIGRATORY HORDES: This will not affect them whatsover.
CITY-STATES: This is cruel, single territory factions will not be harmed whatsoever by this, and are supposed to benefit from this
LOCAL POWERS: These are the entities who are supposed to benefit from this, making it so that if they fight well enough against bigger factions, they will be able to preserve more if not all of their territory even though they lose the war.
REGIONAL POWERS: The first true debuff to annexation occurs here, Regional Powers, once the peace treaty screen is reached, will only be able to annex territory per 100 manpower that they have left (final number undecided), however, annexation will not cost any actual manpower. For Regional Powers, it will simply look at the amount of manpower you have and limit the number of territories you can eat based on that. This will also make barracks and training camps more important as an expansionist power, while a player should have no problem with this, this will slow the Rome of any regional power attempting to become the European Juggernaut.
MAJOR POWERS: Now for these guys, the manpower requirement will actually cost manpower in order to annex territories, 100 per territory. This will not be crippling, considering how most major powers are pretty good on manpower production, often getting 500 a month, but this will incentivize making subjects, I hope.
GREAT POWERS: The manpower requirement will be increased to 500, if you think this is harsh, seriously, as a great power, you are NEVER running out of people to fight for you, it is one of your biggest advantages.
SPECIAL RULES
1: Wars between 2 regional powers will not need manpower in order to annex territory, in wars like these, the regional powers are usually the final boss of each other before they increase their territory rank. Wars such as these usually find both evenly matched and therefore having a manpower cost apply in this circumstance would result in the losing power not really being knocked down from their defeat, and the victor not really being able to benefit.
2: Wars of Imperial Conquest and Civil Wars are also exempt from any manpower costs entirely and would operate as normal.