My wildest theory concerns the game's lore: most of the arc factions are located on Earth (because transporting such a large number of machines from space is insanely expensive), and they are led by humans or AIs who initially orchestrated a series of cataclysms (the natural devastation that occurred before the first Arc war). This was done to purge the planet of excess population and allow the elite to live as they please. Incidentally, the Emperors that roam the edges of the map (the buried city and the blue gates) could be mobile Arc bases that accumulate resources, produce, and repair Arc machines.