Why did the struggle for equal rights intensify after World War II?

During WWll, with white men fighting overseas, African Americans were able to get better job opportunities, and a new law passed saying that blacks and whites had to be in integrated units in the army. But, when the war ended and black soldiers returned to America they weren't greeted with a hero's welcome and instead were treated like all other blacks - they were forced to be segregated. This change from almost equality to none at all really fired up the Civil Rights Movement in the 1950's and 1960's.