The lives of African Americans were affected by World War I in two main ways, one of which can be seen as good and the other of which was less so.
On the good side, the war encouraged African Americans to move to the North. This was the beginning of the “Great Migration.” The war helped to get African Americans to move from the rural south to the urban North. This allowed them to have a great deal more freedom than they had previously had. This can clearly be seen as a good thing because the rural South had been a fairly oppressive place for African Americans.
On the bad side, the war also led to some degree of racial intolerance. This is likely to have been caused by the fact that African Americans were now living in places where they had not previously lived. As African Americans moved North, there was some resistance to their presence by some elements of the white communities in the North. One of the most famous of these was a race riot that took place in Chicago in 1919.
Thus, World War I expanded the possibilities that were open to African Americans but, at the same time, exposed them to some degree of animosity in the North.