Alliances

Alliances and non-aggression pacts are the two most common forms of pacts between rulers. A non-aggression pact is an agreement between two rulers to not declare war on each other. An alliance is an improved pact based on an existing non-aggression pact, and is more powerful by allowing rulers to be called to war.

Non-aggression pacts

A non-aggression pact is an agreement between two rulers not to attack each other. Most non-aggression pacts are created by a marriage or betrothal:

• Characters always have a non-aggression pact with their spouse.
• When two rulers negotiate a betrothal or marriage involving close relatives, they automatically form a non-aggression pact.
• Two rulers can negotiate a non-aggression pact based on an existing marriage involving their close relatives.

A non-aggression pact between a vassal and a liege prevents the liege from revoking the vassal's titles, and prevents the vassal from joining or creating a faction. Also, a ruler who has a non-aggression pact with the defender cannot be called to arms by an ally in an offensive war against them.

Alliance

Alliances are additional agreements to call each other into most wars.

Form alliance

• Must be a close relative OR have a non-aggression pact
• Cannot form alliances with your vassals or your lieges

The following AI reasoning applies to both the "Negotiate non-aggression pact" and "Form alliance" interactions.

Factors	Tooltip	Description
Opinion	+10 to -10?
Same Dynasty	+2
Same Interests	+2
Common Enemies	+2
Political Concerns	~+10 to ~-10	Seems to be related to "RP Friendship" or "RP Hostility", a hidden value (relation?) shown only in debug tooltips. May mean they CB against you (even when negotiating an alliance atop a non-aggression pact)?
Base Reluctance	-3	-25 (if this is the only factor other than opinion, need 26 opinion for Yes)
Alliance breaker	-5	AI is unlikely to accept alliances from alliance-breakers.
Too busy conquering the world and you're next	-10	Expanding horde

Call to arms

See also: Diplomatic actions#Call to arms

Rulers are expected to accept calls to arms with any rulers they have an alliance with. Rulers may also receive call to arms from fellow rulers who have the same culture who are defending themselves from another culture. Nomadic and tribal vassals can also receive call to arms from their liege, as can tributaries and suzerains.

Bug note: If you declare war against your liege (ex. Independence) you CAN call in allies in other realms (as long as there's no NA pact or truce involved) but these realms don't show up as callable in the Declare War screen.

Restrictions

• Faction rebellion leaders cannot call in allies, except for claimant rebellions.
• When fighting a fellow vassal, can only call in other rulers with the same liege. (Exception: if the "fellow vassal" is a faction rebellion against you, can call allies from other realms!)
• Cannot call vassals of your enemy, except in "revolt against tyranny" wars.
• Cannot call your enemy's liege. (99% certain - edit if incorrect).
• Cannot call allies into an offensive war in which a ruler has a non-aggression pact with the defender.
• Can call both a liege and their vassal, if you're allied with both, but it only works properly if you call the liege first.
• Cannot call allies if you are at war after plotting to revoke a vassal's title.

Accepting or declining

Declining a call to arms in an alliance:

• costs a large amount of prestige.
• adds the character modifier "Alliance Breaker", lowering diplomacy by 5 for 10 years.
• adds the general opinion modifier "Alliance-Breaker", lowering opinion of you by -25 for 10 years. (Stacks.)
• adds the opinion modifier "Dishonored Alliance" to your ally, lowering their opinion of you by 30 for 5 years. (Stacks)
• breaks the alliance.

Additionally, the AI is less likely to accept alliances from alliance-breakers and will consider dissolving any alliances it has with them.

Declining other calls to arms has a minor prestige cost:

• -25 prestige for a offensive war.
• -100 prestige for a defensive war.
• 0 if the belligerents are allies.
• 0 for a suzerain declining a tributary's call to arms.

Accepting a call to arms against an attacker you have an alliance with will break that alliance.

Ally orders

As a primary participant in a war, you are able to give orders to your allies. AI allies will perform the orders they receive as long as they don't decide to prioritize other wars.

There are four orders:

• Siege - order ally to siege the selected county (accessible from Province View)
• Attach Army - order ally to attach to the selected army (accessible from Selected Army window)
• Focus on Sieging - order ally to siege strongholds (accessible from "Allies in Wars" tab in the Military View)
• Focus on Hunting Enemy Armies - order ally to hunt for enemy armies (accessible from "Allies in Wars" tab in the Military View)

The "Allies in Wars" tab in the Military View lists all allies which you have in ongoing wars, along with their current orders (if any).

See also

• Defensive pact - Special pacts created to combat threatening characters.
• Tributary - a relationship created through use of the use of the tributary casus belli.
• Rules of Engagement - Dev diary discussing major changes alliances and the introduction of non-aggression pacts.
• As you wish... - Dev diary discussing ally orders.

Warfare

Troops

Levies • Retinues • Mercenaries • Holy orders • Event troops • Hordes • Adventurers

Battles

Combat • Combat tactics • Commanders • Raiding

Concepts

Alliances • Casus Belli • Claims • Crusades, jihads and great holy wars • Factions • Attrition

Characters

Personal attributes

Attributes • Traits • Piety • Prestige • Culture • Religion • Dynasty • Nicknames • Opinion

Actions

Diplomacy • Decisions • Education • Marriage/Breeding • Regency • Favors

Objectives

Factions • Ambition • Plot • Focus

Infamy

Assassination • Tyranny • Banishment • Execution • Imprisonment • Title revocation • Bribes

Other

Council • Courtiers • Disease • Succession • Alliances