The economic advances that almost all Americans made during the 1920s, including some African-Americans, might have been enough to kickstart a civil rights movement, if the Depression hadn't immediately destroyed the tiny black middle class and distracted the nation for more than a decade. Blacks were hit especially hard during the Great Depression, struggling through with sharecropping in the South, and relegated largely to the service industry elsewhere and hard labor in northern factories. While the economics of the rest of the country prevented social advancement, it also for the most part kept racism, unlike how it had been in the 1920s, at a less violent level. That is not to say the Ku Klux Klan was not still active.
As the Depression gave way to World War II, large numbers of African-Americans joined the military or were drafted, just as it was for the rest of the country's population. While fighting in segregated units, and rarely sent into combat, black soldiers served honorably and fought well in units such as the Red Ball Express (blacks made up 75% of transport units), the Tuskegee Airmen, and armored units. They served primarily in Europe and North Africa. They also experienced difficulties adjusting back to a civilian life after the war in a society that still, legally and socially told them they were second class citizens.
In the 1920s, African American culture had flourished thanks to the Harlem Renaissance and several groups were created to fight against racism and segregation (Marcus Garvey's Universal Negro Improvement Association was one of them). The years of the Great Depression, however, threw back African Americans into poverty and segregation. Because of the general economic depression, African Americans were employed only in the most humble and least well-paid jobs. Unemployment and racism were extremely high in the North too. It was estimated that their life-expectancy was ten years less than for whites. The years of the Hoover Administration did not lead to any progress for African Americans and the President himself demonstrated racial insensitivity rejecting anti-lynching laws and nominating John J. Parker, a supporter of black disfranchisement, to the Supreme Court (his appointment was eventually rejected by the Senate).
The case of the Scottsboro Boys was an example of how racism was still institutionalized. In 1931, nine African Americans were arrested and charged with raping two white women. An all-white jury convicted the boys within two weeks of their arrest and sentenced them to death. Although evidence that the women were lying was soon available the case went on until 1950.
African Americans were an important part of the New Deal coalition and the election of Roosevelt marked an improvement for them. New Deal relief agencies and programs helped African Americans to face their economic hardships. The President appointed a group of African American advisers to the White House, the so-called "Black Cabinet". Yet, because of the widespread racism, the New Deal record in race relations remains mixed. Federal financial aid to white planters who took land out of cultivation were rarely shared with black sharecroppers who were instead evicted out of the land. Roosevelt was also unwilling to alienate white southerners so he refused to support laws against lynching and to allow African Americans to vote.
The massive enrollment of African Americans in the American Army during the Second World War allowed them to achieve important steps toward racial equality. Yet, African Americans still had to serve in segregated units and at several military bases racial riots broke out.