I think we could scratch the alien contact, make the whole thing human conflict. Instead of interstellar, we could compress the setting within our own solar system. The conflict could be a resource/territory war, the catalyst being become uncontrollable population growth. Earth would be the gemmed resource source but it's a constant battlefield. Another conflict could be that not all civilians were relocated out of Earth, making a rebels quiet prevalent. Other planets and moons were terraformed but still lacking great amount of resources; barely any fighting, mostly riots and small skirmishes but no full out war. Political seats are probably found in Mars, colonies in many various other location. Mining colony in Mercury (Solar Power), Europa (Water), Titan (Fuel), etc..

Just something out off the top of my head.