Complex sentence: In the mid- 20th century, phenomenology and humanistic psychotherapy made self-esteem gain prominence again, and it took a central role in personal self-actualization and in the treatment of psychic disorders.
Split into simpler sentences: In the mid- 20th century, the rise of phenomenology and humanistic psychotherapy led to renewed interest in self-esteem. Self-esteem took a central role in personal self-actualization and in the treatment of psychic disorders.