EU4: How To Handle Aggressive Expansion & Coalitions

Coalitions are extremely dangerous. They can hinder your expansion or even ruin a campaign out of nowhere.

They can be formed by nations with the outraged attitude towards you. This attitude is the result of high aggressive expansion on your part.

Just like Napoleon, if you rapidly expand at the expense of your neighbors and disregard diplomatic truces, said neighbors will band together to stop your warmongering.

What is Aggressive Expansion?

Aggressive expansion (simply abbreviated AE) is a game mechanic simulating the negative diplomatic impact of your warmongering actions. At its core, it is a negative opinion modifier.

It occurs when you:

• Directly conquer land
• Vassalize or enforce a personal union
• Declare a war without a casus belli
• Violate a truce
• Demand an heir of your dynasty on a nation’s throne

No-CB wars and truce-breaks should be generally avoided. Using favors to demand an heir is not a common interaction and doesn’t result in a lot of AE anyway.

Hovering over the symbol on the bottom right of the peace deal screen shows nations that will end up with more than -50 AE opinion of you.

Your aggressive expansion will mainly be the result of peace deals that expand your nation. The exact formula for calculating AE is quite complicated. The base number depends on the following:

• The CB used
• The development of the land conquered
• Your nation’s “administrative efficiency” and “aggressive expansion impact” modifiers
• Whether or not the provinces belong to a non-cobelligerent

Then, this number is further modified and applied individually to neighbouring countries. The exact formula is the following:

• Religion mod is based on the target’s religion compared to the loser’s religion (NOT YOURS)
  • 50% for same religion
  • 0% for same religious group
  • -50% for different religious groups
• Culture mod is based on the target’s culture compared to the loser’s (NOT YOURS)
  • 50% for same culture
  • 25% for same culture group
  • 0% for unrelated culture
• Infidel mod is 50% if the target has the same state religion as the loser, and your country is in a different religious group. Otherwise, it’s 0%
• HRE mod is 50% if both the conquered province and the target country are part of the Holy Roman Empire
• Distance is the in-game distance between the conquered province and the closest province of the target country, rounded to the nearest multiple of 100 and capped at 400
• Ally mod is 2/3 if the target nation is allied to you, else it’s 1
• Subject mod is 10% if the target nation is your subject, else it’s 1

A peace deal inside the HRE where it’s easier to accumulate high AE

How To Keep AE Low

In all cases you need to plan your expansion to target different religious groups and cultures.

If you conquer a good number of Catholic provinces in Italy, it would be wise to allow some years to pass so that AE with Italians ticks down. In the meantime, you can conquer Muslim provinces in Africa. The Italians will barely care about those, and vice-versa.

AE ticks down by 2 per year and it is affected by “improve relations” modifiers. You can get such modifiers and speed up this process in several ways:

• Prestige (Improve relations: from -50% at -100 prestige to +50% at 100 prestige)
• Hiring a diplomat advisor (Improve relations: +20%)
• Unlocking diplomatic idea 4 (Improve relations: +25%)
• Assigning the “Establish communities” policy in a trade node (Improve relations: +15%)
• Several national ideas
• Missions and events
• Certain Government reforms

Another useful modifier which directly reduces base AE is “aggressive expansion impact”. This can be acquired by:

• Prestige (AE impact: from +10% at -100 prestige to -10% at 100 prestige)
• Unlocking espionage idea 2 (AE impact: -20%)
• Several religion-related interactions (e.g., controlling Curia for Catholics)
• Several national ideas
• Missions and events
• Kashi Vishwanath temple in Varanasi for Hindus only (AE impact: -10%)
• The Grand Palace of Bangkok (AE impact: -10%)

Handling Coalitions

Your options, in order of most to least preferable, are the following:

• Ensure they never form at all
• Attack them while they still have few members
• Diplomatically make members abandon the coalition
• Fight them and attempt to secure an agreeable deal

All the options will be explored in this article, outlining some exploits in case war is inevitable. Detailed focus will be given to avoiding them, as prevention is always better than cure.

Preventing Coalitions from Forming

Coalitions against you can only form if there are at least 4 nations that fulfill the following criteria:

• Has no truce with you
• Is not allied to you
• Has rivalry or outraged attitude towards you
• Has -50 or worse aggressive expansion (AE) opinion against you
• Is not part of another coalition

Essentially, to completely avoid a coalition, you need to keep your aggressive expansion (AE) low and prevent nations from flipping to outraged attitude.

How To Avoid Nations Getting Outraged

A nation will join a coalition against you ONLY if its attitude is set to outraged or rivalry towards you. Sadly, you can’t efficiently do much for the rivalry part.

A nation will not turn outraged unless its opinion of you is negative. This means you should have your spare diplomats improving relations with nations that are close to that threshold.

Dissolving Coalitions

The most straightforward option is declaring an offensive war on one of the coalition members when it is still forming. A well-timed war when the coalition still has only 4-6 members is ideal.

Aim for a white peace, creating at least a 5-year truce between you and the involved nations. This renders them ineligible to join a coalition while the truce lasts.

Another route is the diplomatic one. A nation will leave the coalition against you if:

• They have a truce with you
• They lose the outraged attitude (usually by reaching +50 relations with them)
• They drop below -50 AE with you, and 2 to 5 years pass or no nation in the coalition has a higher than -50 AE modifier
• They feel that the entire coalition is a lot weaker than you and your allies (very rare occurrence)

Fighting Coalitions

If war is inevitable, you should prepare for a long ordeal. It is hard to peace out of such a war. Your enemies cannot be separately peaced out and they all have a modifier of -30 towards their desire for peace.

An exploit you can abuse is giving up your allies’ land. Beware, this can only happen if their provinces are occupied by the coalition. Simply allow your enemies to occupy that land and offer a generous deal that involves none of your own provinces!

Another exploit is the “100% subject annexing”. It involves the following:

1. Have a diplomat working towards annexing a vassal of yours
2. Reach close to 99% process towards annexation
3. Concentrate development or seize a province from them to get the process over 100%
4. Before the month ends, peace out the coalition, releasing this vassal in the peace deal
5. The vassal will get annexed anyway as long as the process is still over 100%

Lastly, it’s worth noting that losing a coalition war does have a consolation prize. Your AE will be reduced relative to the development of the provinces you were forced to return or release as independent nations!