Post Apocalyptic? I think a burnt-out Earth qualifies. The Afterglow was predicted, and along with the ruined atmosphere and scorched earth it took many. Mankind was prepared but options were low. With a global population of just 750,000 the ships set off for Eros, the one Moon capable of sustaining human life. Sustainable. At a push. Harsh environments. Hostile lifeforms. Rich in minerals. New Earth quickly fell back into its old ways. Wealth/Poverty. Upper Class/Lower Class. Literally