This tool can report on or modify the diplomatic relationships (i.e. war vs. peace) you have with other contacted civilizations. Note that a civilization is only at peace if both you are at peace with them and they are at peace with you.
diplomacy all <RELATIONSHIP>
diplomacy <CIV_ID> <RELATIONSHIP>
See current diplomatic relationships between you and all other contacted civs.
diplomacy 224 peace
Changes both your stance towards civilization 224 and their stance towards you to peace.
diplomacy all war
Induce the entire world to declare war on your civilization.