"Attachment theory describes the dynamics of long-term relationships between humans. Its most important tenet is that an infant needs to develop a relationship with at least one primary caregiver for social and emotional development to occur normally. Attachment theory explains how much the parents' relationship with the child influences development. Attachment theory is an interdisciplinary study encompassing the fields of psychological, evolutionary, and ethological theory. Immediately after World War II, homeless and orphaned children presented many difficulties, and psychiatrist and psychoanalyst John Bowlby was asked by the UN to write a pamphlet on the issue which he entitled maternal deprivation. Attachment theory grew out of his subsequent work on the issues raised."