Planetary combat will take place at a lower granularity than games like HOI4, but higher granularity than a game like Stellaris. As such, the planetary combat system will be "region-oriented" more than "unit-oriented." I.e. rather than a large part of the skill of the game being how, precisely, you move individual units around, it will focus more on how much and what type of "military pressure" you assign to a given region.
Combat will be drawn out over a longer period of time per-instance than traditional games. I.e. rather than a combat instance representing one battle before the losing units are dislodged, a combat instance will represent the sum total of all battles, skirmishes, operations or other military interactions between two competing forces in a region.
Combat victory is not black or white. In previous titles, for example, Nation A would dislodge Nation B from Region X, and Nation A would then become the sole "owner" of Region X. In Exo, Nation B will not get entirely "dislodged" from Region X, but both nations will compete for relative Presence in the region, which gives them a proportional Advantage in that region, buffing things like Supply throughput, war score or any other reason you might want to control a region. Rather than having a concrete military "owner," a region will have a list of competing powers with various levels of Presence. The only case in which a nation is truly "dislodged" from a region, is that in which the nation either decides they have lost so many resources that they can longer try to compete for the region, or if the nation truly has no more resources left to dedicate.
Combat instances are resolved through a tick-based dice-roll system. Every day (or some other interval deemed fitting), fancy dice are rolled to calculate the daily change in relative Presence, determined by some equation inputs being all relevant stats of all present combat stacks.
All units in a given region belonging to one nation are said to exist in the same Combat Stack. Stacks can be composed of an arbitrary quantity and variety of military units, all of which contribute to that stack's core values. E.g. the player might develop a new tank, build 1,000 of them and assign them to Stack A, at which point Stack A's overall stats would be modified accordingly.
Core Values