Diplomacy

(This page is for Classic ruleset. For Diplomacy in the Multiplayer ruleset click here.) 
In order to establish diplomatic relations with another player, either AI or human, you must first meet them. To meet another player entails having one of your units be adjacent to a city or unit of that player.
Once you have met another player, you can engage in diplomacy with them as follows:
* Go to -> (or hit the key)
* Select the player you wish to engage in diplomacy with
* Click the button
* Using the menus, decide on what you want to give another player, or what you want the other player to give you (see pacts).
* If the player is an AI player, and they are not cooperating, you can usually find out why by trying to arrange a peace or alliance with them.
While you can arrange a meeting with the players you are in contact with, you can't have more than the most basic intelligence about their civilization without establishing an embassy either by pact or with a diplomat.
==Diplomats==
See also Diplomatic actions
Once your advances provide you with diplomats, and later with spies, you can observe and manipulate other civilizations more subtly than is possible with simple military observation and intervention. Both units are fragile and must move cautiously — often under guard — to survive. The more aggressive actions can spark a diplomatic incident if perpetrated against a civilization you're not at war with; this is sufficient provocation to allow treaties to be revoked under representative government.
Two actions require your unit to approach a lone enemy unit and attempt to enter its square (these actions cannot be attempted on a stack of units):
* Bribe Unit. In exchange for gold, a foreign unit may be persuaded to join your civilization. This action doesn't work if the enemy governs as a democracy. Bribery may be attempted even when not at war, but will cause a diplomatic incident. The cost depends on several factors:
** increases with wealth of the enemy civilization;
** increases with enemy unit production cost and veterancy;
** decreases with enemy unit hitpoints;
** decreases with increasing distance from enemy capital;
** half if enemy unit is a Settler.
* Sabotage Enemy Unit. Only the spy may sabotage an enemy unit, reducing its remaining hitpoints by half if successful. Sabotage may only be attempted when openly at war. After successful sabotage a spy is instantly returned to the nearest friendly city.
All other actions require your diplomatic unit to reach an enemy city alive and attempt to enter it. Diplomats can attempt only one diplomatic act, whose success or failure brings them to their end, while spies are more hardy and often survive their mission. Enemy diplomats or spies in the city will oppose any hostile action. Either your diplomat or the defending diplomat will die. If the defending diplomat dies, you lose one movement point and may try again. The actions available at an enemy city are:
* Make embassy. Both diplomats and spies always succeed when you ask them to establish an embassy. An embassy gives you permanent contact with that civilization. At any time your embassy can provide you with basic intelligence about their government, treasury, trade ratios, and technology. An embassy also allows you to propose pacts to the other player, as described below.
* Investigate city. Your unit will report the status of the city, what units and buildings are within, and what it is currently producing.
* Sabotage city. Your unit attempts to destroy either one of the city's buildings, or all of its work towards its current project. Diplomats will select their target randomly, but spies can be directed towards a specific goal (with a reduced chance of success). Once built, Palaces and Wonders cannot be sabotaged, and attempts to sabotage City Walls or any building in a capital each halve the chance of success. Sabotage may only be attempted when openly at war. After successful sabotage a spy is returned to the nearest friendly city.
* Steal Advance. Your agent will attempt to learn the secrets of one technology held by the other civilization that you lack. Only one advance can be stolen from a city by Diplomats; Spies can steal more than once, but a city becomes more resistant each time it is stolen from. Diplomats steal a random technology, while you may direct a spy to steal a specific advance (with a reduced chance of success). Theft may be attempted even when not at war, but will cause a diplomatic incident. A successful spy is returned to the nearest friendly city.
* Incite city rebellion. In return for gold a foreign city will change allegiances and join your empire, bringing along all nearby units that call it home, but reducing its size by 1. Units in other cities remain in the enemy's control, but units outside cities are lost to both players. Incitement may be attempted even when not at war, but will cause a diplomatic incident. After inciting rebellion successfully a spy is returned to the nearest friendly city. This action doesn't work if the enemy governs as a democracy, or for capital cities. The cost depends on several factors:
** increases with wealth of the enemy civilization;
** decreases with increasing distance from enemy capital;
** increases with present unit and building production costs;
** half if city is empty;
** increases with city size (modified by happiness of individual citizens);
** half if city is in revolt or enemy civilization is in anarchy
** double if city is celebrating;
** decreases if the city was originally yours, or (less) if it is not currently owned by its original builder;
** increases if city has a Courthouse.
* Poison city water. Only the spy can commit this atrocity, and only in war; it empties the city granary and kills one citizen. A successful spy is returned to the nearest friendly city.
==Pacts==
Players can make informal requests, agreements, and threats across the in-game chat channel, but to transfer actual property they must arrange a pact (and of course AI players can only negotiate through a pact). This can be done while the players have contact or may be initiated by a player who already has an embassy with the other. The window this brings up lets each player build a list of items he is offering alongside a list of what he will receive in return. These can include:
* A copy of your current map — showing either all the terrain you have discovered, or just which squares are ocean and which are land without revealing specific features, or both.
* Technological advances you possess.
* Cities in your empire (except the city with your palace), which will take with them any units that call the city home.
* Gold from your treasury.
* Access to your vision — everything your cities and units can see as the game unfolds. Unlike the other items, this is a persistent ability, and must be cancelled in your player list when you no longer wish the other player to see what you are doing.
* An embassy.
* A cease-fire, peace or alliance treaty.
Only if both players indicate satisfaction is the pact concluded and the transfer of goods made.
==Diplomatic states==
===War===
The default state with any player is war.
Unlike most other diplomatic states, war is declared unilaterally by one player on another; thus, declaring war only requires that you have already met the player once or he has declared war on one of your allies. To declare war on an opponent, cancel any treaties with that player until the War state is reached.
Only the War state allows one to attack a unit or to take a city without inciting a revolt.
Enemy units impose zones of control. Cities can be incited to revolt with no disapproval from the senate.
===Cease-fire===
Sometimes, war becomes too costly for both parties. Cease-fire can then be agreed, which after 16 turns will lead back to the diplomatic state of war.
The first time you meet another AI player, it will always offer you a cease-fire treaty.
Under representative governments, the senate will block an unprovoked attempt to declare war again before the end of a cease-fire; the only way to do so is to dissolve the senate by inciting a revolt, and break the treaty in the ensuing anarchy. (However, the Statue of Liberty allows you to break a treaty and restore order in the same turn.)
In this diplomatic state units impose zones of control.
===Armistice===
If you wish to have a permanent peaceful relationship with another player, you may sign a peace treaty. For a transition period there will be an armistice. Like ceasefire, it has a countdown of 16 turns, but unlike a ceasefire ends up in the peace status when the time runs out.
This transition period allows time to move units that would be disbanded under Peace outside of the other player's borders. The AI will always insist on some turns of ceasefire, then armistice, then peace, and will use the armistice to move its units out of the other player's territory.
Breaking an armistice drops you to war. Again, under representative governments, the senate will block an unprovoked declaration of war.
In this diplomatic state units impose zones of control.
===Peace===
A peace treaty is a step towards alliance. It comes into effect after 16 rounds of armistice if no incidents occur.
When a peace treaty kicks in, all military units belonging to peace-treaty players inside your border are immediately disbanded. They cannot send military units through your borders, and non-military units are prohibited from most actions. Breaking a peace treaty drops you straight to war.
Again, under representative governments, the senate will block an unprovoked declaration of war.
Peaceful units impose zones of control and can't be attacked.
===Alliance===
Alliance treaties come with obligations, and you won't be able to ally with a player that is at war with a current ally unless you break the first treaty. If one of your allies declares war on another, the alliance with the aggressor is automatically broken (unless the agressor is your teammate, since team is treatened as an unbreakable alliance). If you have allied two players in cease-fire and it expires, you break alliance with both of them. 
Zones of control don't apply and allied units can enter the same tile (including city and transport). Thus, cities can't be bribed by a diplomat entering in them.
Breaking an alliance drops you to armistice treaty, giving each player time to move their units out of the other player's territory before a new peace treaty kicks in and disbands units.
Again, under representative governments, the senate will block an attempt to break an alliance without provocation.
== Senate and Casus Belli ==
Senate presents in nations that have "Has_Senate" effect (in many rulesets, Republic and Democracy have it always, and other nations that have nuclear weapons between UNO wonder is built and Apollo Program is built). If you really need war and can't explain it to your Senate, you may start a revolution disbanding it (so, Statue of Liberty effect of free government change effectively neutralizes your Senate's ifluence). Removing shared vision needs not Senate approval.
If you have Senate, sometimes it still approves war (or general lowering of diplomatic state), but only if the player in question has provided you a Casus Belli. In v.2.6, it is provided in the following cases:
* Any hostile diplomatic action is performed or attempted out of war time this or the previous turn;
* An alliance is broken due to a war between a player's allies (given until turn end to the side(s) you break alliannce with).
Since v.3.0, you have effects "Casus_Belli_Caught" and "Casus_Belli_Success" that govern will you provide a casus belli by a specific action, failed or performed (the spy may still be caught afterwards) respectively; effect value 1 gives casus belli to the victim, 1000 gives it to every player (but both only for current and the next turn). Casuses belli provided within a single turn don't accumulate.
== AI diplomatic behaviour ==
AI love is a counter of general virtue of a specific AI player to cooperate with a specific human player. It equals 1 by default and since you have met the player may go from -1000 to 1000. Its current value towards you is described in the "Nations" tab by a word, from "Genocidal" to "Worshipful". You can't sign a cease-fire if you are at -400 or below (border case lies inside "Belligerent"), you can't form an alliance unless you are at least "Respectful" (>100), there are other factors of course but AI love is still important (generally, a basic gold for agreement of an AI on doing something is squared difference between current AI love and a level required for doing it voluntarily divided at 10). Want for entering war with you is reduced on around 1/2000 of current love value if it is positiveThe basic want is, simplified to say,100 x num_of_your_cities_and_settlers + 20 x num_of_your_citizens + 8 x your_total_shield_surplus + 6 x your_total_trade_surplus + your_total_buildings_shields - 200 x num_ai_settlers
This value is doubled if you have started building your spaceship and reduced at 1/10...1/3 of its value due to the desire to keep current diplomatic state, and after applying love effect it is divided on 4 again if you are allied, and furtherly reduced if you are far away. The value is reduced onint(your_gold/5000) x num_of_your_cities + 100 x max(num_your_techs - num_ai_techs, 0) + sum_attack_rating_your_units - sum_attack_rating_ai_units,
where attack_rating = basic_utype_attack_power x hp x basic_fp. If you are the best of available targets by the result of these calculations and it's positive, the love to you is reduced on this value or at least 50. And everybody hates the leader of space race, no variants.. To improve AI love, you may give the AI nation gifts (make treaties where all clauses are beneficial for the other side), or build an Eiffel Tower that brings you some AI love each turn by an effect.
AIs like when you fight with their enemies. If neither you nor your allies are in war with the AI or its allies and you don't provoke the AI, the love autoomatically grows (but hardly over 800 if you are not allied). Providing a casus belli costs you 180 love points, and waging a direct war decreases AI love 15 points each turn (mind, "waging war" means not actually killing units but that your diplomatic state is "War", so try to make peace with AIs when you meet them before the contact turns run out or a thousand years later legends will turn you into the evil embodied in this nation's mind). Note that each your unit that AI can see on its territory costs you 5 love points each turn (up to 30 points or 60, if you ally its enemy), even if you are allied!
If the AI decides a war with any player, it starts a countdown and begins preparations. The countdown value in turns is map area in thousands of tiles plus some constant (0 to 4) dependent on the war reason; its stop value is -1 but it can go below when the war starts (then it will count up for 2 to 19 turns until the AI will accept any treates). Your allies will inform you when they are going to attack somebody, and will be angered if you won't support them joining this war. Also, AIs have several general explanations of why they start a war; for example, they will blame you for agression against their ally even if it was you whom the ally attacked first out of mere bloodlust. If the AI has no special reasons to go for a war with a player (space race leadership or providing a casus belli when the war countdown reaches its stop), then its aggression is modified by ai trait trait_aggressive: it will declare war to the most hated player if its love is below 10 x sqrt(trait_aggressive) - 300 and the countdown is over.
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Diplomacy