Europa Universalis IV: Developer diary 43 - Artificially Improved

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Game Director (Victoria 3)
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Nov 15, 2007
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Today for the 43rd development diary for Europa Universalis IV, we're bringing in a very special guest: The AI or Artificial Intelligence of Europa Universalis IV. The AI, of course, is responsible for controlling all the nations that are not under the reins of a player, and has received a number of face-lifts and upgrades from past games. This is a look at some of the more major changes and improvements it has benefitted from.

As mentioned in dev diary #17, Europa Universalis IV gets rid of much of the previous randomness in conducting diplomacy. You make a proposal and the AI country responds Yes or No with a detailed breakdown of its reasoning. This makes it apparent to the player why the AI nation will not accept an alliance, and what (if anything) they can do to get them to change their mind.


The AI also follows this system when dealing with other countries: AI nations will not offer alliances to countries whose alliance offers they would decline and will not bombard the player with requests that they know an AI would refuse, getting rid of much of the diplomacy spam that could happen in previous EU games.

The AI's ability to understand the various diplomatic interactions has also been improved, and it will now make use of certain diplomatic interactions that were previously the sole domain of the player, for example selling provinces when it is in its interests to do so.

The AI in Europa Universalis has strategic goals: Countries it wants to ally, provinces it wants to conquer, neighbours it wants to subjugate. These goals were largely invisible in previous installments of EU and could result in frustration on the player's part as the nation they just sent gifts turns on them without an obvious reason. In Europa Universalis IV, the AI's strategic goals towards a particular country are factored into an 'attitude' which reflects its long-term view on that country.


In the screenshot above, we can see that Bohemia has the 'Threatened' attitude towards Austria. This is a rather complex attitude where Bohemia will both try and ally with Austria and seek out alliances with their rivals, all in order to secure their independence against the threat Austria poses.

As indicated by the red blood drop, if Austria was played by an AI it would have the 'Hostile' attitude towards Bohemia, meaning that they would most certainly reject an alliance with Bohemia and actively seek to conquer them.

Attitudes affect almost every part of the AI's thinking including what diplomatic proposals they agree to, which nations they seek to befriend and what concessions they will seek in a war. One very special attitude, 'Outraged', also drives the formation of coalitions, as described below.

Coalitions have changed since they were first brought up in dev diary #23. All the previous restrictions on who can form a coalition have been removed and replaced with the single restriction of only being able to be in a coalition against one nation at any given time. Coalitions no longer have a 'leader', but are simply a group of countries that have declared themselves united in opposition against an aggressively expanding nation.


As discussed in previous dev diaries, Aggressive Expansion is a negative relations modifier that you get with other nations when you conquer territory, force-vassalize or usurp the thrones of other nations. The size of the relation hit depends on your size, your distance to the nation, and their cultural, religious and strategic interest in the provinces and countries that you conquered.


The more your relations drop, the more likely that the country will change its attitude to 'Outraged', representing anger and resentment towards your aggression. An AI country that is Outraged may take the initiative to form a coalition against you, and once formed, countries that hate or fear you may choose to join in even if they themselves are not Outraged. If you declare war or are declared on by any member of the coalition, all other members will automatically join in and a player who lets their AE grow out of control may find themselves fighting some very large coalitions indeed.

War & Peace
Another change towards transparency is the replacement of the old War Capacity value with War Enthusiasm. War Enthusiasm is a number showing you how much the AI wants to stay in the war, and what it thinks of its chances to accumulate more gains or turn a losing war around.

When negotiating peace with the AI, War Enthusiasm acts as a direct modifier on warscore in determining whether they will accept. If they have 10 warscore and 10 war enthusiasm, they will require a peace deal worth at least 20 to say yes. If they have negative war enthusiasm, you will likewise be able to demand deals that are better than your current warscore, though there is a limit to how much you can demand.


A common complaint about the AI in previous EU games is that it is easy to fool: Even if it manages to defeat you in a war, you can offer it a variety of useless but costly concessions instead of the province that it actually declared war for. This has been improved in Europa Universalis IV with the addition of a level of importance the AI places on each possible concession.


Items of great importance, such as taking core provinces or acquiring the wargoal, are shown with a green thumbs-up, indicating that the AI will value them at their full warscore cost in a peace deal. Items of some importance, such as taking provinces for its allies or an offer of gold are shown with a yellow hand indicating that the AI will only value them at a fraction of their warscore cost. This means that if you want to give the AI a bunch of things that it doesn't really want you will have to give up a lot more than if you just give it the things it went to war for in the first place.

Items that the AI absolutely does not want such as landlocked isolated provinces are shown with a red thumbs-down. Offers containing such a concession will always be rejected.

The AI's ability to command armies has also been improved, particularily in regards to allies. Vassals and AI allies who lack the army strength to operate independently will attach their armies to the war leader's troops, combining with them to form powerful coalition armies. The AI's ability to coordinate action between its armies has also been improved, as well as its ability to give priority to important provinces, especially the wargoal.


Large AI nations in Europa Universalis IV have a new trick up their sleeve: Hunter-Killer armies. Hunter-Killers are specialized armies that will avoid sieging in favor of hunting down enemy armies and wiping them out to the last man. When there are no enemies in sight, Hunter-Killers will instead act as protection for friendly sieges, lingering in nearby provinces ready to move in if the enemy should threaten its besieging allies.

Lastly in this dev diary we'll talk about options. The difficulty and aggressiveness settings from previous EU games have been replaced with AI Difficulty and Handicap.


AI Difficulty
The AI Difficulty option determines the skill level at which the AI operates and how it behaves towards the player. It has the following options:
Easy: The AI plays at a reduced skill level and acts less aggressively towards non-AI nations.
Normal: The AI plays at its full skill level and will treat player and AI nations the same way.
Hard: The AI plays at its full skill level and acts more aggressively towards non-AI nations.

Note that because the AI is more aggressive towards the player this does not mean it will start suicide wars or refuse to ally them simply because of the difficulty, but it does mean that they will react more harshly to players accumulating Aggressive Expansion, for example. AI Difficulty does not provide any economic, diplomatic, military or otherwise bonuses to AI or Player nations regardless of the setting.

The Handicap option controls which, if any, nations will receive economic, diplomatic and military bonuses. It has the following options:
Player: All non-AI nations will gain economic, diplomatic and military bonuses.
None: No nations receive any bonuses.
AI: All AI nations will gain economic, diplomatic and military bonuses.

Bonus: How Paradox’s Crusader Kings II to Europa Universalis IV save converter will work - Interview at PC Gamer

ps. Now we hope you feel ready to bring civilization out of the Dark Ages :)
If that is correct, please feel free to pre-order our game Europa Universalis IV here:


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Colour me very very impressed, especially by the Hunter-Killer armies. I think they've made my day, no more tricking the AI while its sieging a useless province.
This sounds great. If you offer an alliance, is there some randomness involved too?

There is some randomness in how the AI builds up its strategies and attitudes, but there is absolutely no randomness in the actual diplomatic interaction.
Brilliant indeed. Now AI has the depth and reason like never before. I hate games where harder difficulty just means everybody tries to kill you from the very beginning. I bow before you.
Lovely! I really can't wait to play with this...

Question: Is it possible to change/weight AI strategies and attitudes via modding at all?

Edit: Handicap: AI sounds to me like it is the AI who receives a handicap. In your description you say it gives them a bonus though? Surely Handicap: AI is equivalent to a player bonus?
I never understood what Lucky Nations did in EU3. What about EU4?
Lucky nations was there to give the Burgundian bastards 6/6/3 generals and god-kings all the time... :mad:
All sounds good to me but I generally play with no handicap whatsoever. By the looks of the screenshots the difficulty options of the AI regarding handicaps will actually be reduced. Unless the screenshot is misleading and there is more handicap options than just none, ai and human for example. As it just says AI I'm assuming what I am. I'm glad there is an actual intelligence level separate from the AI or human handicaps though. Also allowing people to play as the same country is a cool little feature.
The AI is probably the most difficult part of any Grand Strategy game. Congratulations for the improvements and keep up the good work. I really hope the EU4 team helps the EvW one after this release. The "know how" should not go wasted and EvW can use a lot of AI insights! ;)