Overextension is an Heir to the Throne and Divine Wind triggered modifier. It strikes nations with low cores/provinces ratios, especially those with a ruler with low Administrative skills. Also, the larger and the more centralized a nation is, the sooner it can strike.
A combination of conditions has to be fulfilled in order to trigger this modifier.
One of the following:
- Have a core to province ratio lower than 50%
- Have a core to province ratio lower than 66% AND a ruler with Administrave skill of 4 or 5
- Have a core to province ratio lower than 75% AND a ruler with Administrave skill of 2 or 3
- Have a core to province ratio lower than 85% AND a ruler with Administrave skill of 1
Additionally, one of the following:
- Have more than 120 cities
- Have more than 100 cities AND Centralization/Decentralization below 4
- Have more than 90 cities AND Centralization/Decentralization below 3
- Have more than 80 cities AND Centralization/Decentralization below 2
- Have more than 70 cities AND Centralization/Decentralization below 1
- Have more than 60 cities AND Centralization/Decentralization below 0
- Have more than 50 cities AND Centralization/Decentralization below -1
- Have more than 40 cities AND Centralization/Decentralization below -2
- Have more than 30 cities AND Centralization/Decentralization below -3
- Have more than 20 cities AND Centralization/Decentralization below -4
NOTE: It appears that the core to province ratio does not take distant overseas provinces into account.
Nation A is a kingdom with an ADM 7 king, 0 centralization and 6 provinces, 2 of which are cored. Should they be worried about their low cores ratio? (2/6 = 0.33 = 33%)
Perhaps they should, because yearly taxes are only collected from cores, meaning they will be short on gold to protect the country. However, overextension is not a danger because that only starts to occur at 20 provinces. Minors will never get this modifier.
Nation B has a king with an administration capability of 8, and its centralization slider is currently at -3. The kingdom currently has 47 provinces, of which 30 are cored. The king wants to know how much he can expand his realm without becoming overextended.
First of all, note that kingdom B is eligible for overextension because of its size and centralization. With his high administrative skill, the king can afford to have up to 50% uncored territory. Therefore, assuming that new territory will not have any cores, the overextension limit will be at 30 / 0.50 = 60 provinces. The king can safely conquer 13 more provinces. Do note that a less skilled heir might not be able to rule this kingdom effectively, and that further centralization would not be a good move at this time!
Nation C is a huge, overextended empire. With an ADM 3 ruler, 300 provinces and only 180 cores, how many provinces should they sell or release as vassals to reduce the turmoil?
At their size and with such a poor ruler, this empire can only sustain a 75% core/provinces rate (i.e. 25% uncored). 180 / 0.75 = 240, so if they want to lose overextension immediately they will have to drop 60 provinces. Of course it is probably wiser to wait it out until more provinces are cored in a few decades. But if increased revolt risk and stability cost is somehow really getting you in trouble, releasing vassals could be a quick way out.