Answer: Desegregation of the military.
Step-by-step explanation:
On July 26th, 1948, President Truman ordered to desegregate the armed forces. It was the Executive Order 9981 which stated that all kind of racist treatment must be abolished and that all people in the armed forces should be treated with equality of opportunities no matter the race, religion or origin.
It was a major achievemt for African-American.