As soon as two Empires become aware of each other they establish a Diplomatic Relation, which lets them communicate, trade, and establish the terms of their coexistence, peaceful or otherwise.
The constant evolution of these Empire's diplomatic relations will progressively unlock new Diplomatic Abilities for each to try and steer the relationship where it is beneficial for them. Empires will submit Treaties, air Grievances and make Demands of each other, and if no common ground can be found, declare War on each other... At least until the public opinion demands a return to Peace !
Each Empire has a relationship with every other Empire in the game, and this relationship is defined to a great extent by its current Relation State. The following Relation States exist:
Most of the diplomatic abilities that apply to relations are defined by the current Relation State, which headlines the diplomacy screens with an Empire. However, diplomatic abilities available to each side can be different, as some Relation States are asymmetrical. For example, the Vassalage state defines a Liege with power over a Vassal.
You can exit or degrade your Relation State at any time, provided your Population’s War Support is above a given threshold -- the populace’s opinions are an important factor in diplomatic interactions. Degrading your relation will increase your opponent’s War Support as their population rises up in arms against you. You will also receive a “Traitor” Reputation Badge unless your own population’s War Support is high enough not just to allow but to actively justify the move.
Each Relation State provides access to a set of Treaties which can be used to further customize it.
The collection of Diplomatic Abilities on each side of a diplomatic relation defines what actions each Empire can perform on the other, both from the World map and the Diplomacy screen, as well as contributing towards defining the costs and consequences of these actions:
Treaties are additional accords added on top of a state of Peace or Alliance, adding or removing one or more diplomatic abilities on both sides of the relation. Like Relation States, Treaties can only be added if both sides agree, but either side can unilaterally choose to end a Treaty. However, doing so provides the other side with War Support. Finally, in diplomatic states where one Empire chooses to forcefully assert their will on others, as are War or Vassalage, treaties are irrelevant.
Treaties are only available within a given Relation State; if you unilaterally decide to leave a Relation State then all your current Treaties are broken, and the other side’s War Support is affected accordingly.
For example, suppose you’re Allied with someone and have signed a Customs Union to trade cheaply with them. If the other party decides to break your Alliance, you will receive the War Support boost for the broken Alliance, and for the Customs Union treaty you had signed on top of it.
Peacetime treaties allow you to:
Alliance treaties allow you to:
War Support represents your population’s animosity against a specific Empire. It is the fuel for war: your people’s morale will be broken if you run out, and they will force you to agree to whatever Surrender Terms your opponent suggests. If you decide that war with another Empire is likely, it is therefore important to prepare for it by trying to fill up the War Support meter as much as possible through Grievances, Demands and Skirmishes, and to keep an eye on it once war has been declared. War Support will also fluctuate during the war, depending on how well you’re doing: winning battles and capturing cities will work in your favor, but ransacking and bombarding the enemy's population will increase their War Support against you.
At the end of the war, The War Score is used to determine how many Surrender Terms can be imposed: if you won the war by the skin of your teeth, you’ll not be able to force many concessions. An Empires’ War Score in a given Turn is based on their War Support at the moment War was declared, their current War Support, and the number of enemy Cities they are currently occupying.
Once the war is over both sides are reset their War Support to zero. War Support gradually increases or decreases back to its equilibrium value during times of peace; people will always be a little bit distrustful of other Empires, but it’s hard for them to stay angry if nothing bad has happened.
The amount of War Support gained and lost in different situations can be affected by Legacy Traits, Civics, Constructibles and Technologies, but also depends on how close your Ideology is to the other Empire’s. Ideology is defined by your choices in Civics and Narrative Events, and your Ideological Proximity is how similar your choices have been to the other side’s.
Treaties, Relation States, and Surrender Terms must be proposed by one Empire and accepted by the other in order to apply. Once you’ve proposed something to a given Empire you’re not allowed to make another proposition for a few turns, so choose wisely. The other side can choose to accept or refuse your proposal outright, but they can also opt to counter it--to propose that you pay them a fixed sum of Money in exchange for their assent. The amount of Money that will be requested is defined by the game and grows along with the Era the two Empires have reached.
Unless you are at war with an Empire, or have signed an Open Borders Treaty with them, you are not allowed to enter Territories that have been attached to one of their Cities. If one of your Armies finds itself in such a Territory then you’ll only be able to specify destinations for them to move which are outside of this Empire’s attached Territories, and your Army will take damage each turn from attrition until it manages to leave.
Borders also protect your Armies from attack: regardless of whether you’ve opened your borders, Empires must declare war on you in order to Attack, Ransack or Bombard targets that are within your attached Territories. Fighting can still take place in neutral or unattached Territories however, provided a non-aggression Treaty has not yet been signed.
On the other hand, Outposts provide only a tenuous grasp over Territories; their borders cannot be diplomatically enforced, and hostile forces can trespass and skirmish with your armies without needing to go to war. An Outposts’ control can still be wrenched away from you, if you’re not careful.
Your actions can result in your Empire earning a reputation for itself. Reputation is materialized as a badge applied temporarily to your Avatar. Badges apply passive effects in diplomacy, notably affecting how much War Support is gained or lost. Some badges provide special diplomatic abilities, however.
You can have the same badge up to three times, with each additional copy of the badge increasing the potency of the passive effects. Each Reputation Badge also has a conflicting badge: if two conflicting badges are earned at the same time then each destroys the other. The full range of badge conflicts is:
Grievancesrepresent crimes committed by one Empire on other, or at least opportunities for the “offended” Empire to act as though they are outraged. Receiving a Grievance provides an initial War Support boost against the perpetrator. Subsequently Grievances that you have against another Empire can either be renounced, as a gesture of good faith, or transformed into Demands. If you do not decide what to do about a Grievance within 10 turns of the offending action’s last occurrence, then it will be considered renounced by default.
What you demand using a Grievance depends entirely on the type of Grievance. There are five types in total, each with its own corresponding Demand type:
Having more unanswered Demands than your opponent raises your side’s War Support each turn, as your people get impatient waiting for a response. If you’re the target of a Demand you’ll want to respond relatively quickly, or your opponent will be able to justify a war against you. If you refuse their Demands, your opponent will be able to immediately declare a retaliation war with no War Support penalties. However, if they choose not to declare war in the same turn as your refusal, then they will be forced to discard their Demands. Refusing can sometimes be an effective way of calling an opponent’s bluff.
Demands can also be accepted in order to avoid conflict. Accepting Demands raises your War Support, as your people are incensed at having to bow and scrape to a foreign power. Finally, any Demands that are still ongoing when war is declared are cheaper to enforce by the winning side when their opponent surrenders. Enforcing prior Demands is much, much easier than adding additional monetary or territorial reparations to the peace conference at the last minute.
A third option is available alongside accepting or refusing Demands--propose that both sides withdraw their Demands in order to defuse the situation. If this proposition is accepted, then all the ongoing Demands are discarded at once.
If a Demand is impossible to meet it is said to be “obsolete” and is converted into an equivalent reparation. For instance, if an Empire had demanded a territory from you, but this territory is no longer yours, the demand will stand but instead of giving up the territory you will be asked to pay a lump sum of money.
An unjustified “Surprise War” can be declared provided your War Support is not too low, but this barbaric act will result in a “Traitor” Reputation Badge. If you want to engage the enemy without receiving a badge, you’ll need to find ways to drum up even more War Support before declaring war.
Once war has been declared no holds are barred, and Armies can Attack and Bombard one another no matter where they are on the map. You can also cross the other side’s Territory, whereas usually you’d have to sign a Treaty in order to do so. The war ends once one side has either accepted or forced the other’s surrender, and a comparison between the two sides’ War Support defines the reparations the loser will have to pay to the winner.
By fighting, ransacking, bombarding, besieging, occupying and so on you can chip away at your opponent’s War Support while improving your own. Bear in mind though that the side which declared the war will lose War Support at the beginning of each turn. The onus is on the instigator to finish what they started.
Cities that are taken during a war don’t immediately become part of the victor’s Empire – instead they are simply Occupied by the invading forces until their annexation can be formally recognized as part of the loser’s terms of surrender. Occupied Cities that are not transferred are, by default, returned to their original owner; any occupying forces still present in these Cities are forcibly expelled from the City.
Until their ownership can be resolved, Occupied cities remain cut off from either Empire's economies. They are unable to build anything, generate no science or influence and only produce food to sustain their population. The invader collects a portion of its Money output thanks to their occupation, however.
Each Occupied City is a drain on their original owner's War Support. Capturing an opponent’s Cities and holding on to them is one of the surest ways of breaking their population’s morale. If an Empire occupies all their opponent’s cities by the end of a turn, they will be able to force their surrender immediately.
Either side involved in a War can propose a set of Surrender Terms -- a list of reparations that they offer to make in exchange for a return to Peace. When drafting their surrender proposal, the surrendering Empire must include the application of previous Demands and, once there are no Demands left to add, additional “bonus” compensations to fully consume the winner’s leftover War Score. If they have nothing else to offer, a default monetary compensation will be calculated automatically.
Upon acceptance of the proposal from the other Empire, all surrender terms will be fulfilled immediately, and peace will be restored. The receiving Empire is free to refuse a legitimate surrender proposition if they find it lacking, but doing so will hurt their War Support and bolster their opponent's.
If one side in a War runs out of War Support, their opponent can force their surrender, choosing exactly which Surrender Terms their opponent will have to agree to.
The Victor is bound by the same rules for drafting a forced surrender: outstanding Demands must be selected first, then spend their War Score selecting additional territorial or political reparations, and finally a default monetary compensation if nothing else can be selected.
Forced Surrenders are unilateral and cannot be refused by the losing side. Once submitted, all surrender terms will be fulfilled immediately, and peace will be restored.
If both sides simply want the war to end, notably in order to deal with threats from third parties, then a White Peace can be signed. This ends the war immediately without any reparations being paid. A White Peace works like any other proposition, so can only be proposed every few turns.