"Need for War" is the name for the decision process AI wizards use to Break Treaty or Declare War towards others, including the human player. To see when this happens, refer to AI to Player Diplomacy or AI to AI Diplomacy.
In order for anything to happen at all, the target of the check must not be the human player, or the game has to progress into turn 100 or later. Additionally, neither wizard can be banished, they cannot already be at War with each other, and they must have Diplomatic Contact.
The process consists of the following five steps, all of which are executed one after another in the order they are listed :
Chaotic war check Edit
If the wizard has the Chaotic personality, there is a Difficulty Level/300 chance of an immediate Declaration of War. However, if the target is the human player, and the Peace Counter is not zero, this effect is prevented. Difficulty Level ranges from 0 (Easy or Intro) to 4 (Impossible) and on the lowest level, this war declaration cannot happen at all. In the 1.50 unofficial patch, the effect of the Peace Counter also extends to AI targets. This Declaration of War will use a different message than the normal version, and will generally mark the cause of the War to be random nonsense, such as the conjunction of stars.
Militarist war check Edit
If the AI has a Militarist or Expansionist Objective, and they do not have a Lawful personality, there is a 5% chance to execute this check. However, if the Peace Counter is not zero, and the target is the human player, this war check is skipped.
Militarist war check in the 1.50 unofficial patch Edit
If the AI has a Militarist or Expansionist Objective, and they do not have a Peaceful personality, there is a 33% chance to execute this check. However, if the Peace Counter is not zero, this war check is skipped. This is different from earlier versions where Lawful was preventing this type of Declaration of War. As such, wizards with the matching personality do not pose a larger threat due to their Objective at all.
If Military Modifier + Visible Relation + Hidden Relation + Personality Modifier - (Difficulty Level *10 if the target is the human player) <= -75 then Move towards War. However, Military Modifier is completely different in this version. Due to that, this war declaration serves the role of starting a war on weak, easy to defeat targets. In general, anyone with a significantly weaker army will be most likely attacked as soon as possible.
This is the minimal amount of Visible Relations needed to avoid such a war declaration if possessing exactly half of the wizard's army strength as the human player :
When possessing only 20% of their power however, the table changes like this :
As visible, it's extremely important to build up army strength quickly if there are Militarist or Expansionist rival wizards around to avoid being dragged into an early War.
Generic war check Edit
There is a 5% chance to execute this check. However, if the Peace Counter is not zero, and the target is the human player, this war check is skipped.
Note that this is an exact copy of the Militarist war check, so having that personality only doubles the check of doing this war check instead of making an actual difference.
Generic war check in the 1.50 unofficial patch Edit
There is a 1/7 chance to execute this check. However, if the Peace Counter is not zero, this war check is skipped.
Note that the Military Modifier here serves a different purpose than in the previous check, ensuring the two checks are not redundant like in the earlier versions. In this formula, Military Modifier is a number between 0-150, the larger the gap in any direction between the two player's Astrologer Military Total Power. Due to this, this war check serves the role to declare war on anyone rising in power to the point they rival the deciding wizard. Players with significantly weaker, or significantly stronger armies are most likely ignored, unless Visible Relations is very low.
Assuming the two wizards have identical armies and a Hidden Relation of 0, these are the required minimal Visible Relation levels to avoid War as the human player :
However, if one of the wizards has only half the army strength of the other, which results in a +50 modifier, the tables changes like this, making it much easier to maintain good relations :
Alliance war check Edit
Check all other AI wizards. If they are at War with the human player, and allies with the deciding wizard, Move towards War against the target wizard at a 10% chance unless they are also our allies or the Peace Counter is not zero. Note that the target wizard is not checked at all in any regards except for not being an ally of the deciding wizard, which is most likely a bug. Either this was supposed to be "human player" as both italic words, or "target wizard" for both. The intended functionality is to honor the Alliance and declare war on the ally's enemy, however the person checked and the person the declaration is sent to will be different, unless the target is the human player. In simple terms, this is a nasty bug which causes AI players to declare war on everyone if they have an ally who is at War with the human player.
In the 1.50 unofficial patch, this is fixed :
Check all other AI wizards. If they are at War with the target wizard, and allies with the deciding wizard, Move towards War against the target wizard at a 1/15 chance unless they are also our allies or the Peace Counter is not zero.
Difficulty war check Edit
If the Difficulty Level is not the lowest (Intro in 1.31 or Easy in 1.40 or later), perform the following :
Count the number of wizards currently at War with the human player. If the number is lower than the Difficulty Level, the Visible Relation with the target wizard is -30 or worse, and the Peace Counter is zero, and random(15) <= abs(Visible Relation/10) then Move towards War against the target wizard.
Note that this again contains the same bug as above. It is most likely supposed to increase the amount of wars towards the human player, or according to a less likely interpretation, increase the amount of wars in general. However, the targeted wizard is not guaranteed to be the same one whose number of wars are calculated. In simple terms, this is another nasty bug which causes AI players to declare war on everyone if their Visible Relations is -30 or worse, as soon the human player is involved in fewer wars than the difficulty level demands.
The 1.50 unofficial patch fixes this by ensuring that the target wizard here can only be the human player. If they aren't, the rest of the check is skipped and nothing happens. Additionally, the chance of taking action is lower, it is only happening if random(60) <= abs(Visible Relation/10).