Following the carnage of World War I, Freud added Thanatos to his theory of instincts. Thanatos, the death instinct, explains human destructiveness. Because pleasure can only be found through the reduction of tension, there must be a drive to reach a state of total quiescence, a state of no tension at all. This is the equivalent of death, hence the death instinct. We now realize that pleasure comes from the build-up of tension as well the release of tension.