In 1941, A. Phillip Randolph threatened to “March on Washington” if then President Roosevelt didn’t desegregate the armed forces and change government hiring practices.
Under pressure to act, President Roosevelt passed the executive order #8802, which established the fair employment practices committee (no discrimination in the hiring practices of the defense industry).
In 1948, Harry Truman was elected without the support of some of the Southern states, which started showing the end of segregation.
In 1947, Jackie Robinson broke the “color line” in baseball.
Thurgood Marshall pushed desegregation even further.