Necessity is the mother of invention, an observation thoroughly sustained in explaining the origins of group therapy. World War II provided the necessity, and military psychiatrists, many of whom were analytically trained, the impetus to begin a new form of treatment for emotional disturbances. Faced with the enormous task of dealing with large numbers of patients, and the impossibility of applying individual psychotherapy in the face of these numbers, the analytically oriented psychiatrists brought together patients in small groups and, thus, gave birth to group psychotherapy.

For psychoanalysts in the military, such as Michael Foulkes, it became important to think of group therapy as an application of psychoanalysis albeit "beyond the couch." This work, in turn, coincided with the extensions of the therapeutic idea and, perhaps, ideology to the family, industry, and the community. The postwar period also saw the development in social psychology of studies of the small group, which made a lasting impact on theory as well as methodology