EXPANSION
Overextension
Overextension is the main factor of expansion stability. It depends on two scores:
- core population score
- periphery population score
Without taking modifiers into account, they are just the population in your core and the population outside of your core, respectively.
As long as your periphery population score is below your core population score, everything is fine. Once the periphery score exceeds 100% of the core population score, you will receive an expansion stability penalty according to a formula which I will explain later.
The scores are affected by a number of modifiers and therefore aren't only based on city population.
The
core population score is multiplied by [current era]+1. That means, even in the ancient era (= 0), every point of core population can potentially support two points of periphery population without any penalties. Since the modifier is era-based, your ability to support a large periphery grows during the game.
Additionally, if a civilization has only one city in their core and is in the classical era or later, they receive an additional core population score equal to the population of that one city multiplied by their current era. This is meant to support civilizations such as Inca or Tibet with a small core that can only contain one city.
The
periphery population score depends on multiple factors. Therefore, for every city a modifier is calculated, which has the initial value of 0 and cannot have a lower value than -1. For every modifier point, the population of the city counts 50% more, i.e. a modifier of 2 means its population counts double. Having a modifier of -1 means the population only counts half. The following factors affect the modifier:
+2 if the city is not on historical territory (so it makes sense to mainly control historical tiles)
+1 if you are not the original owner of this city (unless you are running Totalitarianism or Warrior Code, or the city is under your control for more than 25 turns)
+1 if you have less than 50% culture in this city
+1 if you have less than 20% culture in this city (those two penalties are cumulative, for a total of +2 if you are below 20%. Native culture counts double within their own cores. Persia is immune to culture-based penalties due to their UP)
+2 when running City States (this civic is only meant for small civilizations)
-1 if the city has a Courthouse
-1 if the city has a Jail
-1 if it is an overseas city and you are running Mercantilism
-1 if it is an overseas city and you are Portugal (their UP)
+1 if it is a historical overseas city an you are running Totalitarianism (to discourage Totalitarianism for maintaining colonial empires)
The stability penalty you receive for every percentage point of periphery population score exceeding 100% core population score is given by the function graphed below:
If you are not a math person, that means that the penalty can be at most -25, and that it grows faster right after exceeding 100% than later on. It works this way to have a diminishing yet growing effect of overexpansion to allow domination games without making stability meaningless when playing for historical victories.
Between stability checks, the overextension penalty can only increase by at most 5 negative points. For instance, if you had a penalty of 0 in the last check and the calculation results in -10, you will still only get a penalty of -5 until the next check.
Razing
Razing cities is the other contributing factor to expansion stability. The score here is very straightforward. You get a -10 stability penalty for every city you have razed. This penalty decays by 2 points every 5 turns. This penalty is global, that means if you accrue -20 raze stability from razing two cities, it still decays by 2 points every 5 turns, instead of by 4.
The exception to this rule are smaller cities. If the city has a population of less than 5, the penalty is -2 * [city population] instead. This exception does not apply to another civilizations capital, which always gives a -10 penalty when razed.
ECONOMY
Economic Growth
The economic growth score is updated every third turn, in which the total amount of commerce produced is compared to the amount from three turns earlier. Has it grown by more than 5%, the score increases, has it shrunk by more than 5%, it decreases. Otherwise the score slowly moves towards 0 again.
At every stability check the score is directly applied to the economy stability.
Some of your civics influence your economic growth stability:
- you receive extra points during economic growth when running Free Market
- you receive no penalties during economic stagnation when running Environmentalism
- you receive less penalties during economic decline when running Public Welfare
Trade
Your cities have trade routes to other cities generating commerce (exports). Other cities have trade routes to your cities also generating commerce (imports). For all civilizations, their total trade volume is calculated, which usually is the sum of exports and imports, but for Mercantilist civs it is twice their export volume instead.
The trade volume is divided by your number of cities, then subtracted a modifier that increases with your era. Effectively, you can achieve a positive score by increasing the trade yield in your cities and securing trade routes with foreign cities.
The trade stability is capped at +10 and -10 respectively.
Economic Systems
Civilizations running Mercantilism receive a -2 penalty for having open borders with a civilization with a higher commerce output.
Civilizations running Central Planning receive a -2 penalty for having open borders with a civilization that runs Free Market.
DOMESTIC
Happiness
Happiness stability works similar to economic growth stability in that it is accumulating every third turn depending on the situation of your civilization. To that end, the happy and unhappy cities in a civilization are counted based on the following criteria:
Happy city: currently celebrates the "We Love the King" day OR its happiness exceeds its unhappiness by at least a quarter of your empire's average city size and it has at least the average city size of your empire
Unhappy city: the city has more unhappiness than happiness OR the extra unhappiness (from all factors except population) exceeds a fifth of the city's population
Some explanatory examples:
A lot of these criteria were chosen so that you would not benefit from global happiness effects such as resources while keeping your cities artificially small, and that actions which cause unhappiness such as slavery will have an impact on stability even with a large happiness buffer.
Note that it is possible for a city to not fulfill either of these criteria, in which case it doesn't count at all for the purposes of happiness stability. A city can also both fulfill the criteria for being happy and unhappy, in which case it counts as happy.
Your happiness stability grows every third turn if you have more happy than unhappy cities, and declines if you have more unhappy than happy cities. This factor cannot exceed -10 or 10, respectively. If the amount of happy and unhappy cities is exactly the same, the value slowly approaches 0 again.
Religion
For religions, two or three percentages are calculated:
- the percentage of cities that have your state religion (believer ratio)
- the percentage of cities that have at least one non-state religion (heathen ratio)
- if you are running Theocracy, the percentage of cities that have ONLY your state religion
Some non-state religions are ignored for the purposes of the second and third ratios ("tolerance").
- civs with Secularism tolerate all non-state religions
- Mughals tolerate all non-state religions because of their UP
- Hinduism and Buddhism tolerate each other
- Confucianism and Taoism tolerate each other
Heathen ratio: You incur neither penalties nor bonuses if your ratio is 30%. Otherwise, you receive -1 stability for every 10% over 30% and +1 stability for every 10% below 30%.
Believer ratio: You incur neither penalties nor bonuses if your ratio is 75%. Otherwise, you receive -1 stability for every 5% below 75% (up to a maximum of -10) and +1 stability for every 5% over 75%.
Theocracy bonus: if you are running Theocracy, you also receive +1 stability for every 20% of your cities that only have your state religion.
Note that while the other factors require you to have a state religion, the religion stability from the heathen ratio also applies when you don't have a state religion.
Civics
Civics stability comes either from running a certain combination of civics or from running specific civics in a certain era or after discovering a certain technology.
Totalitarianism + Autocracy: +5
Totalitarianism + Central Planning: +3
Totalitarianism + [any religious civic except Secularism]: -5
Central Planning + Industrialism: +2
Central Planning + [any labor civic except Industrialism or Public Welfare]: -5
Egalitarianism + Republic: +2
Egalitarianism + [any labor civic except Public Welfare]: -3
Egalitarianism + Environmentalism: +2
Egalitarianism + Secularism: +2
Capitalism + Representation: +2
Capitalism + Free Market: +3
Capitalism + Guilds: -5
Environmentalism + Industrialism: -5
Theocracy + Fanaticism: +5
Theocracy + Organized Religion: +3
Theocracy + Secularism: -7
Theocracy + Egalitarianism: -3
Vassalage + Warrior Code or Levy Armies: +3
Vassalage + [any other military civic]: -5
Vassalage + Capitalism or Industrialism or Public Welfare: -5
Vassalage + Dynasticism: +2 in the Middle Ages
Vassalage + Agrarianism: +3 in the Middle Ages
City States + Vassalage or Absolutism or Egalitarianism: -3
City States + Guilds: +2
City States + [any economic civic except Self-Sufficiency, Guilds and Mercantilism]: -5
City States + Militia or Mercenaries: +2
City States + [any military civic except Militia, Mercenaries and Naval Dominance]: -3
Absolutism + Republic: -5
Absolutism + Mercantilism: +3
Absolutism + Organized Religion: +2
Absolutism + Dynasticism: +2 in the Renaissance
Republic + Representation: +2
Warrior Code + Dynasticism: +2
Warrior Code + Fanaticism: +2
Autocracy + Standing Army: +3
Vassalage in the Middle Ages: +2
Vassalage in the Industrial Era or later: -5
Theocracy in the Industrial Era or later: -5
Pantheon in the Classical Era or earlier: +2
Pantheon in the Middle Ages or later: -2 * [current era]
City States in the Classical Era or earlier: +2
City States in the Industrial Era or later: -5
Direct Rule or Vassalage or Absolutism after the discovery of Democracy: -5
Slavery or Agrarianism after the discovery of Democracy, unless running Totalitarianism: -5
Any Organization civic except Totalitarianism and Egalitarianism after the discovery of Communism: -5
Self-Sufficiency or Guilds after the discovery of Corporation: -5
Slavery after the discovery of Economics, unless running Totalitarianism: -5
Mercenaries after the discovery of Nationalism: -5
Warrior Code after the discovery of Military Science: -7
FOREIGN
A couple of factors contribute to your foreign stability rating:
For every neighboring collapsing civ that you have open borders with: -3
For every collapsing vassal: -5
For every unstable vassal: -2
For every solid vassal: +3
For every vassal when running Vassalage: +2
For every defensive pact with a higher ranked civilization: +5
For every open borders treaty with a civ with your state religion: +1
For every open borders treaty with a civ with a different state religion: +2
For every second civilization you can contact: -1
Being the worst enemy of a higher ranked civilization: -4
For every neighbor you are at war with while running Autocracy: +2
For every civilization with different state religion you are at war with while running Fanaticism: +3
For every civilization with the same state religion you are at war with while running Fanaticism: -2
MILITARY
All military scores are calculated for each your civilization is in.
Conquest Stability
This factor depends on the number of cities you have conquered from this civ compared to those you have lost to it. Cities are worth more if the owner has less of them, i.e. losing a city has a larger impact if you don't have a lot of them in the first place.
Battle Stability
Similar to conquest stability, the battles you have won are compared to the battles you have lost. In either case, a battle is "worth" as much as the defeated unit's power rating. How much battle stability you get or lose depends on your overall military strength - the stronger you are, the less of an impact a singular battle has in either way. Battle stability decays while a war lasts.
War Weariness Stability
Your war weariness is compared to your enemy's. If it is larger, you receive a penalty proportional to the difference. This penalty also decays while the war lasts.
Barbarbian Losses Stability
You receive a -1 stability penalty for every battle you lose against a barbarian unit. This penalty also decays over time.
