Okay, a quick guide for how the stability mechanic works so people can actually judge what's going on.
First of all, stability checks don't happen periodically anymore. They are triggered by one of the following events:
- losing a city
- razing a city
- researching a tech
- becoming a vassal
- vassalizing another civ (+)
- declaring war / being declared war on
- making peace (+)
- changing civics
- changing state religion
- moving your palace
- building a wonder (+)
- starting a golden age (+)
- receiving a great person (+)
Under certain circumstances, the check is canceled because the civ is currently immune to it. The main reasons for this are that the civ has just spawned, just received a crisis and is therefore protected or is in anarchy or a golden age.
During the check, the civ's stability score is calculated. This score only depends on the current state of the civ without any permanent influences. The score is the sum of the results in the five categories expansion, economy, domestic, foreign and military. More details on the score calculation follow later on.
Then, a threshold is determined with to which the score is compared. The threshold is higher at higher stability levels and lower at lower levels. This has the result that unless something changes within your civilization and therefore your score at the next check, you eventually arrive at a certain level and stay there. Here's what can happen:
score > threshold + 10: your stability level increases by one
threshold < score <= threshold + 10: nothing
threshold - 10 < score <= threshold: a crisis occurs
score <= threshold - 10: your stability level decreases by one, a crisis occurs
Checks triggered by events marked with a (+) can only result in a stability increase, never in a decrease or crisis.
A crisis affects your civilization negatively in some way. The type of effect depends on the category your score was worst in, and the severity of the crisis depends on your stability level. The level is reduced before the crisis starts in the last case above, so it's one level more severe than the level you entered the check with. Here's how the stability levels correspond to the crisis levels:
solid -> no crisis
stable -> minor crisis
shaky -> moderate crisis
unstable -> severe crisis
collapsing -> terminal crisis
A terminal crisis always results in complete collapse no matter the type. As you can see above, it's possible to be on collapsing stability level and still never experience a crisis, so it's not guaranteed that you collapse on this level (but very much possible until your situation improves). Also, solid makes you completely immune to crises until your stability drops again. Here's a short summary of the effects:
EXPANSION
Minor: a random city secedes
Moderate: all cities in foreign territory secede
Severe: all cities except your core secede
ECONOMY
Minor: lose 10% of your current research (first in gold, then in beakers)
Moderate: lose 50% of your current research, one turn of anarchy
Severe: lose 100% of your current research, three turns of anarchy, cottages degrade, great people points are reset
DOMESTIC
Minor: one turn of anarchy, 25% chance for all cities to have unrest for three turns
Moderate: three turns of anarchy, 50% chance for all cities to have unrest for five turns
Severe: five turns of anarchy, all unhappy cities secede
FOREIGN
Minor: two random open border agreements are canceled
Moderate: five random open border agreements are canceled, all defensive pacts are canceled, all peace vassals are freed
Severe: all open border agreements are canceled, all defensive pacts are canceled, all vassals are freed
(every canceled treaty also includes a relationship hit and makes the civ not want to talk to you)
MILITARY
Minor: all cities lose their defenses
Moderate: all cities lose their defenses, 25% chance per unit to desert
Severe: all cities lose their defenses, 50% chance per unit to desert, cities secede to civs you're at war with if they're in their target area
Here's a short summary of what can affect your stability score in the different categories:
EXPANSION
- ratio of core vs. non-core population (cities on historical territory are weighted much less than ahistorical, conquered, or foreign core cities)
ECONOMY
- economic growth (change of total commerce compared to 10 turns earlier)
- penalty for trading with richer civs under Mercantilism
- penalty for trading with Free Market civs under Central Planning
DOMESTIC
- relationship of happiness/unhappiness in your empire
- number of unhappy cities
- civic combinations
- contemporary/outdated civics
- religious unity (state religion in all cities, not too many non-tolerated non-state religions)
FOREIGN
- open borders with collapsing civs
- stable/unstable vassals
- defensive pacts with stronger civs
- being the worst enemy of a stronger civ
- having furious relations with someone
- being at war while in Autocracy
- being at war with heathens / brothers of faith while in Fanaticism
MILITARY
- winning/losing wars
- losing military strength compared to 10 turns earlier
