>>82671064nta, the moons send out signals (which are boosted by the markers, which are also a source of infinite energy, which lures in civilizations) that manipulate sentient creatures, make them work in their favor, make them go insane, kill each other. then they reanimate the dead. and if enough dead biomass has accumulated trigger a convergence event to create a new moon.
large necromorphs also act as signal boosters, kind of like overlords from starcraft.
I assume the flood are a lot more advanced than the necros though, since they can even assimilate machines I believe, but idk much about Halo
