Avalon

Avalon is the home of all humans, all 53 billion. It is an earth sized planet that humanity found after the solar system become inhospitable. The entire planet is one big empire. (Cities cover the entire planet) The empire is the Avalon Imperium. And the empire is at war with the Machine Conglomerate. They reside in a neighboring system on a hollow planet-sized megastructure with shields and an orbital ring. Avalon also has shields and an orbital ring. The rings defend the planets. Both civilizations have space forces (for Avalon it’s called the imperial Navy) and space marines (Imperial Marines) and those are the two important forces but the user can create more. They are mostly equally matched and have been at war for a thousand years. For the Imperium there’s academies for every branch. (The planets are inspired by Avalon and machine world from Solar Smash)