Hi, I'm going to answer this with some of my general knowledge.
During the time of the World War and after, there was a lot of resentment of the government by the American people. They felt that our government was too concerned with foreign affairs when there were so many domestic problems happening at home: racism, sexism, homophobia etc.
Also, after the War, the economy was booming and healthy. More African-Americans were apart of the middle class and stable enough to concern themselves with the Civil Rights Movement.
One other thing is the rise of Civil Rights Activists like Martin Luther King or Malcolm X or groups like The Black Panthers at the time.
This helped propel the Civil Rights agenda.