World War I was a turning point in African American history. The trickle of blacks moving out of the South after 1877 increased enormously as war industries and the decline of European immigration combined to produce demands for labor in Northern cities. The coming together of large numbers of blacks in urban areas, the exposure of some African Americans to European whites who did not hold the same racial attitude as American whites, and war propaganda to "make the world safe for democracy" combined to raise the hopes, dreams, and aspirations of blacks.

Segregationists countered this optimism with an upsurge of lynchings, riots, and other antiblack violence after World War I, however. The Ku Klux Klan was revived and gained impetus in Northern as well as Southern states during the 1920s. These actions blunted the efforts of blacks in politics, but the changing attitudes among blacks found other forms of expression. The 1920s was a period of notable accomplishment in African American literature, music, and art, and race consciousness increased. The latter is reflected in the writings of the influential black leader Marcus Garvey, founder of the Universal Negro Improvement Association and an ardent proponent of black nationalism.

African Americans initially were less affected than whites by the Depression of the 1930s because the economy of the black community was already depressed. Before long, however, the worsening economic conditions hit blacks, as the group at the low end of the economic scale, the hardest. Reforms attempted by the New Deal almost exclusively concerned economic matters. No effort was made to alleviate the hardship suffered by blacks because of their racial-minority status. In New Deal efforts to aid the poor, however, blacks encountered the first assistance from government since Reconstruction. Franklin D. Roosevelt's sensitivity to the existence of racism, coupled with growing disaffection with the Republican party, caused more and more voting blacks to support the Democratic party. This was often an uncomfortable decision for blacks, because under the seniority practices followed by Congress, control by Democrats placed avowed segregationists in major positions of legislative leadership. The shift continued, however, and since the New Deal period African Americans have increasingly voted for Democrats.

With the outbreak of World War II, wholehearted African American support was given to the war effort with the hope that the fight against Nazi racism would weaken racism in the United States. Of the 891,000 blacks who joined the military, approximately half a million served overseas. African American combat units included the 92d and 93d divisions and a small group of air force pilots. As in World War I the majority of blacks were organized into service units, and many were never trained in the use of basic weapons. In an attempt to encourage and improve job training for minority-group workers in war industries, President Roosevelt established a national Fair Employment Practices Committee. The war ended, however, with no major attack on discrimination in employment and in labor unions, and Jim Crow practices persisted in many parts of both the North and the South.