Diplomacy

Relations

• You are at peace or at war with each civilization you have met. At war, units of the two sides cannot share a tile and fight on contact.
• Each AI leader holds a mood towards every civilization it knows, counted in mood points from -20 to +20. It starts at 0 and is simply the sum of the reasons below, so it changes the moment one of them does. The diplomacy screen shows every leader's mood and reasons, towards you and towards each other.
• Moods read as Friendly from +12, Pleased from +4, Angry from -4 and Furious from -12. Anything between is Neutral. An Angry or Furious leader starts thinking about war.
• Peace: a leader greets a civilization it has just met with +2 for the first 20 turns. After that, remaining at peace is worth +1, and another +1 every 25 turns the peace holds, up to +3. A war starts the count over.
• War: -12 for as long as the war lasts.
• Your integrity: above 50% it helps, below it hurts, twice as steeply.
• Religion: a civilization that shares your state religion likes you (+10), and the faith's founder likes you more (+14). A leader following a faith you founded holds +14 for you as its founder. One following a different founded faith does not like you (-14).
• Trade: every active deal with them is worth +2, up to +6. Cancelling one early costs -6 for a long while.
• History: each past war leaves a grudge of -6 (-4 more for a war you started), down to -12. Holding cities that were once theirs costs -8 per city, down to -16, for as long as you hold them. Denouncing them costs -6 while it stands; breaking a treaty with them -6. Attacking through a peace treaty -12.
• Friction: borders that keep changing hands cost 2 for each flip. A leader who envies your cities holds -1 against you, deepening by one for every 10 more envy your cities earn (bigger, richer cities with more goods, buildings and wonders), down to -6. Distance tempers envy: a leader whose nearest city is within 12 tiles of yours feels all of it, one 36 tiles or more away only 25% of it, with a straight fall-off between.
• Friends and enemies. Declaring war on a civilization a leader is Friendly with costs -16 with that leader (-8 if it is only Pleased with them) for a long while. Fighting the same enemy as a leader is worth +4 per shared enemy, up to +6, for as long as both wars last.
• Fear: a leader whose army is no more than 50% of yours is afraid of you. Fear lifts a bad mood just as far as Neutral, never further. A frightened leader will not start a war with you alone, but it may still ask a friend to fight you together.
• Contempt: on the harder difficulty levels, a leader whose army far outmatches yours, and that can reach you by land or sea, looks down on you. The stronger it is and the more aggressive its leader, the worse its mood towards you.
• Excommunication: a leader you have excommunicated holds -4 against you for as long as it stands.
• When a leader's mood towards you falls to Angry you are told, with the reason that tipped it.

War and peace

• Declaring war costs integrity unless you denounced the target first and gave the warning time to stand.
• An angry leader does not act on a passing mood: it starts a war only after 3 turns in a row of anger, against a civilization worth the fight that its armies can reach over land, past no neighbor that has refused them passage.
• While a player is away, the leader minding their civilization keeps the peace. It defends, but denounces no one, declares no war and joins no pact.
• A peace treaty ends a war and binds both sides for 20 turns. Neither may declare war while it runs.
• A leader that is winning will not accept peace just because you ask; one that is losing badly will offer it, or surrender outright. Losing a city alone does not make a leader sue for peace while it is still clearly the stronger side. It fights on to take the city back.
• No leader talks peace in the first 10 turns of a war, whoever started it, unless its armies are being routed.
• A leader whose cities you hold wants them back, as long as one of them can be reached over land and it is strong enough to try. It goes to war to retake them, and for the first 30 turns of that war it will not sign a peace that leaves them with you.
• A war in which nothing happens for 20 turns, no battle and no city taken, is one nobody is winning. The leader will offer peace, and accept it.
• Open Borders lets each side's units cross the other's territory. A leader whose armies must cross your lands to reach an enemy will ask you for it. A leader will not open its borders to a civilization at war with one of its friends.

Joint wars

Two civilizations can agree to go to war with a third together. The pact sets the day, chosen by whoever proposes it. At once, or in 15 turns, with both preparing until then. An AI partner declares on the day itself, and at once if its partner has already gone in. The target is not told; it learns of the war the way it learns of any other, from the denouncements that come before an honest declaration. When the day comes, each side has 3 turns to declare. Once both have, the pact holds them at war for 10 turns: no separate peace, and each must fight the target at least once while the pact stands. Breaking any of it is considered a breach of contract. Backing out or never declaring costs -10 integrity (an AI partner: -8), obtaining a separate peace -8 (-10), leaving the fighting to the partner -4 (-4). A contract breach is public. For 60 turns the breaker is known as a backstabber, every AI leader who knows it thinks less of it (-2), and none will sign a pact with them. A partner who kept their word is remembered too (+4). An AI keeps its word: it will not make a separate peace unless the war is lost. AI leaders ask the friends they are Pleased with to join the wars they would rather not fight alone, and join a war themselves when they like the one asking (or hate the target) and the two together are a match for it, but not against a civilization of their own state religion, unless they have a grievance of their own against it.

Asking

Every request is throttled: a proposal the other side refused or ignored cannot be repeated for a number of turns (peace: 10 after a refusal, 30 when ignored; open borders: 20 and 40; trade: 15 and 30; joint wars: 20 and 30).

Excommunication

Tired of a civilization's requests? Excommunicate it, from the diplomacy screen or the Treaties tab of an audience: from then on it can ask you for nothing at all, no trade deal, no treaty, no joint war, not even peace, until you lift it. You can still put your own requests to it. Other players can be excommunicated the same way. An AI leader resents it (-4).

Read on

• Integrity and Denouncements
• Treaties and Trade Deals