<P> During most of the 20th century , mental illness was believed to be caused by problematic relationships between children and their parents . This view was held well into the late 1990s , in which people still believed this child - parent relationship was a large determinant of severe mental illness , such as depression and schizophrenia . Today , the belief is held that the child - parent relationship is of small importance in terms of causing mental illness compared to biological and genetic factors . So , the perceived causes of mental illness have changed over time and will most likely continue to alter while more research is done in this area . </P>
in most cases what appear to be the two main causes of emotional or behavioral disorders
biological genetic factors