The correct answer to this open question is the following.
Economic opportunities expanded for African Americans, Mexican Americans and women during World War 1 because most American men had to go to the war front after the United States entered World War I, on April 6, 1917. So these Americans went to war, leaving plenty of job opportunities for African Americans, Mexican Americans, and women in the manufacturing plants. During this time, many immigrants arrived in the United States because the country needed extra hands to work in the factories producing war supplies and weaponry.
