It 1948, President Truman signed an Executive order:
"It is hereby declared to be the policy of the President that there shall be equality of treatment and opportunity for all persons in the armed services without regard to race, color, religion, or national origin."
During this time period there was a lot of discrimination and segregation. Blacks and whites were still not equals. For example, blacks sat in the backs of buses, attended different schools, etc. America was very segregated.
In 1955, a man named Emmitt Till, was brutally murdered for supposedly whistling at a white woman. Two white men were acquitted by a white jury and bragged about the murder later. That same year a woman named Rosa Parks refused to give up her seat on the bus to a white person. This caused a lot of outrage. This is when the Montgomery Bus Boycott occurred. The next year buses were desegregated.
In 1964, President Johnson signed the Civil Rights Act of 1964 which prohibited discrimination based on sex, color, religion, or national origin.
In 1968 Martin Luther King was shot to death by James Earl Ray.
These are just a few of the things that occurred. There is so much more.