There are a few algorithms to determine your actions, I believe the most simple one is the minimax (https://en.wikipedia.org/wiki/Minimax).

Here is my five minutes explanation to give you the main idea of the way it works (probably not really good, but there are thousands of great articles on the internet about it).

First must define an evaluation function that given an army, determines one score for each strategy, this is probably a hard and subjetive task and pretty likely you will need to put a lot of twinking on it. For instance of points you can check to determine the score of an strategy:

- you can check how well defended are the airfields, the shipping and the factories.

- In case of a direct conflict how many resources you will lost and compare it with enemy loses, you may also include some factor for resource aquisition (for instance, I will lose more resources, but I have a lot remaining, while my enemy has nearly none, so this is good for me) and rate of production (I will take 2 minutes to recreate the lost unities, my enemy will take 4, so this is good for me).

After you got this function, you run it for the possible strategies for your army, then you check the counter mesures your enemy would take and run the function to those, and so on. In the end you will have a decision tree (look at the wikipedia article, this forum won't let me post in svg format). Now you pick the best result when it is your turn, and the worst when it is your enemy's turn (hence minimax). In the end you will filter the path of the best strategy. Keep running this algorithm from time to time to assert if you should keep your plan.

This is one of multiple ways, I believe it is the most simple one, and a good one because it will make your logic more organized (as you just need to twink the evaluation function), otherwise you may end up in an if-else hell.

I'm going to ignore the general engineering issues with your approach and just focus on what's hanging you up the worst: thinking about how to design AI.

The best place to start is emphatically NOT to pick some arbitrary algorithm or architecture and try to cram your game into that framework. That's a recipe for a lot of pain and wasted time.

Instead, you should think about the "I" part of AI. A handy mnemonic is "What would I do?" - not just "I" in the sense of an abbreviation for "intelligence", but also "I" as in "me."

Think about how you would play the game you're writing an AI for. Think about what kind of decisions you're making, and try to analyze why you make some decisions rather than others. The more detail you can pinpoint, the better.

Sooner or later you will reduce your game-playing to a set of rules: when this happens, react that way; and so on. Distill these into general principles (hostility means attacking; fear means running away; etc.) and you have the seeds of your AI. Once you understand how and why the game is played, you should have a pretty easy time turning that into code.


At this point - and no sooner - you can look for architectures that suit the particular rulesets you've come up with.

the behavior of the example above would be as follows:

at the start of the war, the AI would go after planes. once the enemy air strength was reduced to 50%, it would switch to factories, unless the merchant fleet was 2/3's dead, in which case it would go after shipping. anywhere along the way, if enemy air power, shipping, or production falls to 10%, it would switch tactics and concentrate on that as a knock out blow.

already one improvement:

irregardless of the strategy (planes, ships, factories) you'd probably want to allocate 10% of your forces to each of the ones not chosen. IE 80% ships, 10% planes, 10% factories, etc.

you'll also want to take into consideration the condition of your air force, shipping, and factories, and what the enemy is doing. if you're low on factories and the enemy is targeting your factories, you'll want to go after planes to protect your factories and avoid defeat.

often times, the checks for avoiding defeat will appear first:

if (half_dead()) run_away()

followed by the checks for achieving success:

if (hostiles_nearby()) fly_to_closest_hostile()

if (hostile_in_LineOfFire) shoot()

The actual task of your AI is providing the combat flight simulator player with fun missions, not winning the war; as its only opponent is a copy of itself rather than a human strategist, it needs to make reasonable and plausible decisions, not particularly optimal ones. Subtly cheating against the player's faction when it's ahead would be a good way to ramp up difficulty for the player and make a campaign last longer. In exchange for not even trying to be optimal, your AI needs to care about what missions the player can choose: among several possible missions of similar type, how can you predict which one is more fun? Is there a good variety of available missions at all times?

The actual task of your AI is providing the combat flight simulator player with fun missions, not winning the war

so its really a campaign and mission generator, not AI to run a "side" in the game.

different, yet somewhat similar.

I did a space flight sim where a politics engine drove something like a dozen campaign generators, which in turn drove something like two or three dozen mission generators. and the mission generators could generate hundreds or thousands of possible missions, before you even got into number appearing and initial placement. the game had something ridiculous like 58,000 different possible missions.

again there, i used an of AI like expert system (the politics engine) to determine what type of campaign to run (similar to air superiority vs anti-shipping vs anti-production in this case). the generator for a given type of campaign controlled mission flow and assigned missions based on current game state, again using its own expert system to choose missions. a mission generator determined things like target type.

so the approach will be the same, but you'll think about it from the commander-in-chief's point of view: "if i were the boss, what strategies would i pursue under which circumstances?". this gives you your AI rules for selecting strategies.

once a strategy is selected, the question becomes: "given that i'm pursuing strategy 'X', what are appropriate missions to assign, and under which circumstances?".

this gives you your AI rules for assigning missions.

then you just code up the rules into your expert systems. one to choose strategy, and one for each strategy to choose missions. no real balancing required. just a little tweaking of the odds of getting this mission vs that mission kinda thing.