Federations are groups of empires that band together for mutual benefit. Forming a federation binds the group as allies and creates an additional federation fleet under the command of the current federation president. Diplomatic relations inside of a federation become more favorable: members do not generate border friction amongst themselves and they build trust with each other to a cap of +100. A federation's name is randomized at creation but the president can change the name at will. In the default map view, all federation members share the same color.
A federation can only be created by an empire that adopts the Federation tradition from the Diplomacy tree. Federation members share 10% of their victory score with each member.
An invited empire must have a positive acceptance score with all existing federation members to join a federation. Hovering over the diplomatic choice will show which empires agree and disagree.
Acting as the military leader of a Federation, the president is the ruler commanding the Federation Fleet. The president is the empire with most Relative Power, and any Federation member that reaches Superior Relative Power over the current president will take control of the Federation. The president has no authority in a Federation's external policy, they only design and command the Federation Fleet.
It is important to note that a Federation president can use the federation fleets for its own benefits alone as long as it does not involve a war, such as defeating a guardian or securing the Sanctuary system. AI members can't judge the player actions as selfish in this case.
Federations feature a special joint space navy in addition to the forces of the separate member empires, under control of the current federation president. federation fleets cost no maintenance and use the Federation Fleet capacity, to which every member contributes with 20% of their naval capacity, up to 500. The Fleets cannot exceed this cap. The Entente Coordination tradition doubles the federation naval capacity contribution of the members that adopt it while not reducing their own further.
The president designs the Federation Fleet ships via a special ship designer available in the federation menu and may use any technology available to any member empire. Regular ship designs cannot be used to build federation ships. The President's empire is responsible for building and commanding the federation fleets. Any AI federation member's research of a component-unlocking technology will auto-update the default federation designs, but not the player-created ones, adding theirs to the list instead. Since their designs are considered newer if you update your federation fleets at this time your fleet will become their design, which can be undesirable.
federation fleets do not have a Command Limit, capping only at 500 because of the naval capacity limit.
If a Federation is disbanded so are all federation fleets.
A Federation acts as a single entity for diplomatic purposes. Diplomacy is based on majority, with an exception of war declaration, which requires unanimous vote from all current members.
Instead of non-aggression pacts, federations can offer and can be asked for an associate status. Federation associates benefit from increased Trust and a +10% Opinion bonus with all the federation members. This can be used as a step before joining to build trust with all members. Federation associate status counts as non-aggression pact for factions such as isolationist faction.
Federation Members cannot declare personal wars but can always propose one to the Federation at any time. Every Federation member must accept for the war to be declared, requiring mutually beneficial war goals unless the targeted empire is hated by everyone. The war declaration menu lists whether a member will be satisfied with the war goals and agree. They can also be asked for demands and if the Suggest Demands button has no effect it means there is no way a specific member will agree to the war, usually because they consider it suicidal.
Of particular note, player and AI pacifist empires can agree to the war, circumventing their no unrestricted wars policies.
Throw out of Federation/Cancel Association Status
If all members except the one being targeted agree, a federation member can be excluded from the Federation. However, due to trust gained, this is unlikely to work with AI Empires unless severe transgressions (like Purges) have taken place. Association Status can be canceled in the same way.
Federation members or empires with Association Status can exit said Federations at any time, without any need to vote. No matter how the relationship ends, an automatic 10 Year Truce will be enforced, and trust will decay per the usual rate.