From Civilization V Wiki
Diplomacy is important in Civilization V. The world is huge and filled with other civilizations whose leaders are just as cunning and determined as you are. Some are honest; others are liars. Some are warlike and others prefer peace. But all want to win.
You can accomplish a lot through diplomacy. You can gain allies and isolate your enemies. You can create defensive and offensive pacts. You can increase your technology through cooperative research ventures. You can end wars that are going badly for you. You can bluff the credulous and bully the timid.
It's a big, tough world out there, and you won't last long if you automatically attack everybody you meet. Sometimes it really is better to talk than to fight – at least until their back is turned and you're ready to launch the big sneak attack.
Who can conduct Diplomacy
You can speak to a city-state or another civilization's leader at any time after you've established diplomatic relations with them. This happens automatically when one of your cities or units encounters one of their cities or units. (In fact, the desire to establish diplomatic relations is one of the driving forces behind world exploration.) After you've established diplomatic relations with another political entity you can speak with them at any time. Though they may not have much to say if they hate your guts.
Note that another civ or city-state may attempt to open negotiations with you, as well, after you've established diplomatic relations.
To initiate diplomacy, click on the Diplomacy Panel button. The Diplomacy Panel will appear, displaying all known civilizations and city-states in the game. Click on an entry to speak with that leader. Alternatively, you can click on a civ's or city-state's city banner to open communications with them.
What you can accomplish depends upon whether you're speaking with a civilization or a city-state.
Diplomacy with Civilizations
When you engage in diplomacy with civilizations, you have these options:
- Declare War
- Click on this button to declare war against the civilization.
- Negotiate Peace
- If you're at war with the civ, you can discuss peace.
- You can negotiate a trade deal with the civilization. Clicking on this button will bring up the Trade Screen.
- You can demand stuff from the other civ. It may comply if you're a lot bigger than it or if it otherwise feels it's appropriate. Or it may declare war on you. You never know…
- This button allows you to open up dialog on a variety of topics. Depending upon circumstances you may do any of the following. The leader's response will depend upon his or her relations with you and their own self-interest.
- Ask the leader to work together.
- Ask the leader to work against another civilization.
- Ask the leader to go to war against another civ.
- Request that the leader not build any more new cities near you.
- Press this to exit diplomacy with the leader.
Negotiating with City-States
City-States are much less complicated than civilizations. You have fewer options when negotiating with them. Generally you can offer them gold or goods, or declare war or offer peace. Sometimes they will ask favors of you.
- DECLARING WAR
You can declare war on a city-state or another civilization through the Diplomacy Panel or by simply attacking one of their units. You can declare war on a civ by entering their territory without an Open Borders agreement, as well.
They can declare war on you in the same fashion.
- NEGOTIATING PEACE
While at war, you can offer to negotiate peace through the Diplomacy Panel. Your opponent may refuse to negotiate altogether, in which case the war will continue. If it's willing to negotiate at all, a city-state will always accept an offer of peace without pre-conditions.
If your opponent is a civilization who is willing to discuss peace, you may negotiate the price for peace on the Trade Table. Depending upon circumstances one side or the other may give the opponent gold, treaties, cities, and/or resources in exchange for peace.
Note that your opponent can also offer to negotiate peace. It's usually a good idea to at least see what they're offering before deciding upon your response