Diplomacy is the means by which the player in Civ IV can interact with other factions, negotiate trade agreements, trade technology, build alliances and gain support for a war. The mechanics are similar to those used in Civ III: things you can trade are displayed on the right of the screen, and items you may ask for in return lie on the left.
Any on-going deal may be canceled after 10 turns without a declaration of war. An on-going item, such as money per turn, may not be traded for an immediate item, such as a city.
This is the list of things, to my knowledge, one can trade in a diplomacy screen. During War, a cease fire or peace treaty may be offered.
Potential Trade Items
The various demands trades are as follows:
- Requires: Currency
This can either be in the form of a one off payment, or a series of payments. The lump sum offered or demanded cannot exceed the total available to that civilization at that time. This prevents you from actually bankrupting anyone. Likewise, Gold Per Turn cannot exceed the faction’s current net gain per turn.
- Requires: Paper
The world map transfers the current map to the other player, and is usually traded by the AI players with another world map.
Open Borders Agreement
- Requires: Writing
This agreement allows you and the other player to send units through each others territory without reprisal.
AI players will never agree to these forms of agreement if they hate the other party the most, or if their attitude towards you is too low. As such, you need to gain their trust first.
- Requires Military Tradition
This agreement provides an agreement between two civilizations that helps deter rogue nations from declaring war. If an enemy declared war against you, all other civilizations will automatically declare war on the attacker. However, the pact is cancelled if either party attacks another civilization.
- Requires Communism or Fascism
This agreement merges two players for the rest of the game. They will share resources and technologies, as well as treaties. This should be done with caution, as any member in an alliance that declares war will force others to join in.
By default, this form of alliance is not enabled. However, it is possible to start this type of alliance at the beginning of the game.
- Requires Alphabet
This allows transferring a technology from one civilization to another. Technology can only be transferred if the requirements are met.
The AI player usually trades technologies one-per-one, with gold to offset the difficulty in research. However, AI players will not trade technologies if they are using it to construct a Wonder or if it is a technology used to win the game. In addition, non-friendly AIs will not trade technology if you have received enough technology from other civilizations and are one of the more powerful civilizations.
A resource provides a special benefit just for having the resource. Extra resources can be provided or traded with other civilizations, which gives the benefit to the other civilization as long as the agreement lasts.
AI players offer resource exchanges one-per-one, but can also cover the resources by an allotment of gold per turn.
Transferring a city is a very significant event. Demanding a city from another civilization is usually seen as a precursor to a war declaration, and AI players are very rarely willing to relinquish a city to another player.
With AI players, there is a limitation on city transfer. While they will accept cities that they owned previously, they won't accept cities if they are in financial trouble or if it is no nearby city that they own.
'Make peace with'
This request attempts to get a civilization to make peace with another civilization.
You can't use this on an AI player to get it to become peaceful to a human player, and you cannot use this if one of the two civilizations is pressing warfare (for example, it is much more powerful.)
'Declare war on'
This request tries the other player to join in a warfare with another civilization. They will not engage in warfare unless they feel they will be victorious, and won't turn the back on any of their friends.
'Stop trading with'
This request tries to get the other player to cancel all agreements with another AI player, including defensive pacts, open borders, and resource trades.
This request tries to get the other player to adopt a certain civics setting.
AI players will not switch over to a civic that will cause anger, and leaders will never switch away from their favorite civic.
This request tries to get the other player to adopt a certain religion.
AI players will only consider switching to religions that are either in greater quantity than the state religion, or that cover at least half of their cities.
With AI players, these are very important. Your interactions with other civilizations, as well as your civics, juxtaposition and religion can affect their opinion of you. This is measured with modifiers. Positive modifiers make them like you more, negative ones make them dislike you.
Positive modifiers are as follows:
- Giving assistance
- Giving tribute
- Accepting their trade offers
- Accepting or adopting the state religion
- Accepting or adopting the favorite civic.
- Providing warfare assistance.
- Fighting against a common foe without being asked to.
- Stopped trading with the worst enemy.
Negative modifiers are as follows:
- Declaring war on them.
- Declaring war on their friends.
- Nuking them.
- Nuking their friend.
- Razing their city.
- Razing a holy city of their current state religion.
- A spy was caught attempting sabotage of improvements.
- Declining to give assistance
- Refusing to give tribute
- Declining to adopt the state religion.
- Declining to accept the favorite civic.
- Not providing warfare assistance.
- Refusing an embargo for their worst enemy.
- Stopped trading with them, especially if recent.
- Made an arrogant demand from them, especially if recent.
- Having close borders, sparking tension.
- Trading with their worst enemy.
- If their rival is a vassal to your empire.
- Poor health religion
Random events (weddings, a diplomatic faux pas, or charitable aid to a starving nation) can also create positive or negative modifiers.