It seems, too, that after a war is when Horror becomes a thriving genre. EC Comics after WWII, the Marvel obsession with vampires and monsters as Viet Nam wound down. It was after WW I that horror movies started up in popularity, like CABINET OF DR CALIGARI and NOSFERATU. During wartime, cheerful escapism is more prevalent; after war, the nightmares have to be experienced to exorcise them.
It's not an exact universal rule, but a trend I've noticed.