During World War II, African Americans were more free than ever before. Many were allowed to fight in the war, which felt liberating to them to be treated the same as whites.
Along with this, when many white Americans were off fighting in the war, many African Americans had the chance to take their jobs while they were gone. During this time, some African Americans worked in factories and other jobs that before would only be allowed for white men.
After World War II, the freedom that the African Americans had previously was gone and they were back to being treated poorly. This caused many Civil Rights Movements to begin to try to regain the freedom they had and other freedoms exclusive to whites.