 The Watcher prevented the moon's inhabitants from reaching the surface and developing technology, but cannot destroy the civilization as it is protected by ten kilometres of ice.News comes from Earth (delayed nine years by the speed of light) that the Swarmers have begun land invasions; the tense superpowers each suspect the other, and escalate into a full-scale nuclear war.The machines, who had attempted to engineer just such a conflict, send their flotilla against the weakened Earth.