What large scale strategies would an interstellar nation use to conquer another interstellar nation?
I'm working on a science fiction setting for a game. I'm trying to write a setting that focuses on man-operated war machines in sight range combat. Everything ranging from fighters to mechs to capital ships would be used and have logical reasons within the setting to steer combat towards that approach.
One of the factions are a group of colonies that had declared independence from Earth decades ago and had managed to win it. These colonies since declared themselves a new interstellar nation with a strong economy, but their military power has always been limited by their low relative population compared to other interstellar nations. Their military doctrines lean heavily into getting the most out of the individual in their military forces and maximizing the survival rates of their pilots and crews (think large war machines with small crew/pilot counts and lots of armor.)
Over the decades since, interest in reclaiming these outer colonies would change with each election cycle, sometimes sparking one of many short lived wars to reunite humanity under one rule. 46
At best, they would manage a stalemate, at worst, they would be pushed back.
I'm trying to figure out what the strategy of the Earth military would be in trying to re-establish control over these colonies. I imagine landing troops wouldn't really work on a planetary scale as they would need pretty much need an occupation force far larger than would be sensible to maintain. Though a strategy of precise military strikes on the ground might work?
I know that taking points of interest might be a factor, as well, factories that produce war machines, shipyards and the like. Anything that might help them establish a foothold in enemy territory.
I should also mention that robotic and other autonomous combatants are specifically outlawed by treaties signed by multiple interstellar nations that I'm still working on the details of. A robot/drone army isn't an option for them.
The only real strategy I can think of is blockading planets and taking control of the system gates to force a world into submission. FTL between systems utilizes artificial wormholes generated by massive gates that are expensive to produce, so it would be easy to control travel to and from a system by shutting off gates.
Armed incursions might only be limited to things like seizing factories, military bases and shipyards to limit the colony's ability to fight back while under that blockade.
What are some other strategies that might come into play in this scenario? 46