What is Post Apocalypse manga?

An anime that takes place on future Earth (or it could be an alternative universe) after a major cataclysm has occurred. World War III, an alien invasion, plague, global warming or some other general disaster are common themes to build a post-apocalyptic world upon, where the effects were severe enough that mankind barely survived.The time frame may be immediately after the catastrophe, focusing on the travails or psychology of survivors, or considerably later, often including the theme that the existence of pre-catastrophe civilization has been forgotten (or mythologised). Post-apocalyptic stories often take place in an agrarian, non-technological future world, or a world where only scattered elements of technology remain. There is a considerable degree of blurring between post-apocalyptic fiction and that which deals with false utopias or dystopian societies.