Why and how did blacks from the south get new opportunities during WW1?

Reason and the way blacks from the south get new opportunities during WW1:

During the First World War, a lot of blacks in the United States of America migrated to a lot of major cities. This was known as the great migration. A lot of blacks migrated to cities like Chicago, New York, Detroit and Pittsburgh. A call was given for people to join the armed forces for the world war one, despite attempts by America to keep away from the so called "chaos which was happening in Europe". People were hesitant to take part in the war. The blacks took this as an opportunity to show case their patriotism and enrolled into the armed forces.