Well, this is a math intensive game, and some calculations are necessary (like how many units you need to keep a newly invaded territory for example), but like Donut said there are way too many considerations that can't be solved just by looking at the math of it. It takes strategic sense, and looking ahead. Consideration of terrain, possible secret allies, how soon you can bring in reinforcements, how to bring a new front to the opponent, etc.
One rule of thumb I go by in the invasion question (what to invade with): I count up the damage output of all the enemy units within striking range of my invasion force, then I add the cash value of how much they get in Guerrilla to this damage total (because Tanks, Mortars, and LAVs give one damage per $). If I don't have more hitpoints worth of invading forces, I don't invade. Then you have to consider how you will keep the invasion past the first turn, though, how you'll keep reinforcements streaming in so they can't drive you out again with that much more advantage.
Founder of The New World Order, and moderator for the Andromeda Clan War.
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