Yuuzhan Vong Rakata Celestials Those three can defeat the Forerunners, Precursors, and the Flood. The UNSC, Covenant, and all other factions are irrelevant because they would be easily defeated by the Galactic Empire, Galactic Republic, Sith Empire, Separatists, Infinite Empire, Mandalorian Empire, or whoever else you wish to fight against them. Star Wars shielding and weapons technology just far surpasses what is in Halo.