What caused industrial psychologists to begin working with the military? 9/11 terrorist attacks u. s. entry into wwi u. s. entry into wwii u. s. involvement in vietnam?

u.s. entry into WWI caused industrial psychologists to begin working with the military.After entering into world war-I there is a need for U.S to train their military and develop the army's strength and capability.Psychological research and treatment are important to national defense. Research can show how to improve military training, job assignment and equipment design. Treatment can help personnel cope with stress. Psychologists conduct research on human behavior and treat patients with mental problems. so,industrial psychologists to begin working with the military.