A Defensive pact is a multilateral agreement to defend against an extremely threatening neighbor. If the subject of the pact attacks one of the members, others will join the war like allies.
Membership in defensive pacts is influenced by threat, a value for each realm that increases during expansion and decays slowly over time.
Each county conquered adds between 2% and 15% threat. The exact amount depends mostly on your realm size(?). Claim and de jure wars generate less threat. Personally inheriting titles when you are already a ruler also increases threat, but at a lower rate than war. A single source can add at most 50% threat.
If your vassals generate threat, some of this threat will be added to your own. This effect is much smaller than the effect of expand on your own, since any given vassal is too small to generate much threat per county.
Threat decays at a rate between 0.21% and 0.4% per month. The exact amount depends on your military strength(?).
Granting independence to vassals decreases threat. This encourages you to release outlying vassals, especially those who provide fewer levies due to de jure structure. Releasing your furthest vassals can also shrink defensive pacts, because fewer foreign realms will be close to your borders.
It is best if you already have a non-aggression pact with the vassal you plan to release, so they can't join defensive pacts(?) and you can request an alliance.
At low levels of threat, defensive pact members are organized by religion group. As threat increases, even infidels will fight together when defending against you.
|5%||Minimum for defensive pacts against you|
|50%||Religious groups other than yours will band together|
|75%||All religious groups band together|
|95%||Even religious heads will join all wars|
- In my ERE game, I see fellow Christians only joining defensive pacts when I have a CB, and even then not always. On the other hand, Pagans far too distant for holy wars are all in the pact. This isn't fully explained by what I gathered below, from reading defines.lua. What am I missing?
Any realm can join a defensive pact against you if:
- Your threat is at least 5%
- They are smaller
- They are within 300 distance, or 400 distance if another religion group
AI will consider joining against you if:
- You could attack me: Less than 80% troop strength and you have a CB (except "Make tributary" or "Humiliate nomad"?)
- You're too big: Less than 20% your size in provinces
- Pact needs assistance: pact is less than 70% strength, an existing member of their religion/culture/dynasty, and you are not
AI will then compute a score to decide whether to actually join:
[(1.0 × provinces) + (150 × threat) + (-1.1 × distance)] * cb_multiplier
They will join with a score above 110 and leave with a score below 70.
There are many things you can do other than simply waiting for threat to decay.
Go all in
When fighting a war that would take you from 40% threat to 90% threat, declare six other wars at the same time. This is your last chance to attack moderately weak realms until (1) you can take on entire regions at once or (2) your threat decays.
Attack targets who are not in defensive pacts
- Attack new realms the day they are created, before they have a chance to join defensive pacts. Make sure you have a CB ready.
- Pick off vassals who are rebelling against their liege.
- If a realm has not yet joined a defensive pact, avoid gaining a CB on them until you're ready to attack. For example, only invite a claimant at the last minute.
- Invade realms that are stronger than you on paper, increasing your de facto power through alliances or by hiring mercenaries and holy orders.
Blitz small members
Pick off tiny defensive pact members by assaulting their holdings very quickly. If you completely occupy the target realm before the rest of the defensive pact shows up, you have 100% warscore and can declare the war over.
The main problem here is that levies cannot be raised when declaring war. Retinues or mercenaries, on the other hand, can be days away from arriving in the province. These professional armies are expensive, but there are many ways to gain wealth.
If a realm is slightly too large for a quick retinue assault, you can use a two step plan. First, find an excuse to be hostile to their armies and holdings. Use levies to weaken them as much as possible. Second, declare war on them and finish them off with retinues.
There are several ways to become hostile to a realm without incurring a truce or getting the defensive pact involved:
- Being allied to their enemy:
- Join an ally in a war where your target is on the other side
- Join a coreligionist in a holy war
- Join a rebelling vassal (
- Being at war with their rebelling vassal
Support vassals in their external wars
- Establish strong vassals near your borders, even if you normally prefer to have weak vassals
- If they need assistance, send them cash gifts, or pick off the armies of their enemies when you are temporarily hostile.
Force realms out of defensive pacts
- Form non-aggression pacts
- It helps to have a large family.
- Use favors to arrange marriages with infidels. You probably won't be able to buy a favor from a ruler who is in a defensive pact against you, but you might be able to buy a favor from their heir for use later.
- You can even create a non-aggression pact with a betrothal, immediately break the betrothal, and attack. This is gamey af.
- Make them your tributary if you can't take a significant chunk of their land in a single war.
- Forcing tributaries to join your wars may weaken them enough to trigger revolts, which you can declare war on freely.
- Keep levies down so that if your ruler dies, you can quickly declare wars to restore tributary status.
Be a vassal
- It appears that when you conquer territory, any defensive treaty formed will be against your liege lord, who is perceived as the ultimate owner of this territory, and won't be triggered by future wars you initiate.
Search defines.lua with the following regexp:
Other PDS grand strategy games have related mechanics:
- Victoria 2 has Infamy. Internally, it is called BadBoy.
- Europa Universalis IV has a more nuanced version of threat called Aggressive Expansion, a relation modifier that indicates how threatened each nation is by your actions. When Coalitions form in EU4, they can act aggressively to dismantle a threat.