The theory of Psychodynamics was created by Sigmund Freud in the late 1800s. Psychodynamics refers to the interplay between the Id, Ego, and Super-Ego, unconscious forces at play, that when in extreme conflict results in disorder. Psychoanalysis was a popular approach designed to both discover and treat the mental disorders of his time.
Application to Clinical Depression
From Freud's perspective, clinical depression was caused by unexpressed anger believed to be unacceptable by the individual. The anger thus becomes, 'turned inwards' through a process called repression. An individual struggling with an over active super-ego (e.g., internal parent), feels shame for the anger they experience towards another. They then repress this anger, energy that is then expressed as depression.