Civil rights and segregation leap immediately to mind. The period you describe was the period that Thurgood Marshall, as the executive director of the NAACP Legal Defence and Educational Fund masterminded a legal campaign against legally enforced segregation, winning U.S. Supreme Court cases like Shelley v. Kramer, 334 U.S. 1 (1948), which prohibited the government enforcement of agreements that prohibited sale of property to racial minorities; Sweatt v. Painter, 339 U.S. 629 (1950) which held that Texas's ad hoc law school for black students did not qualify as "equal" for the purposes of "separate but equal" education and finally, and most notably in terms of discussion in the wider population Brown v. Board of Education, 347 U.S. 483 (1954), which overturned the whole concept of "separate by equal," requiring that public schools be integrated.

Brown provoked enormous backlash in the South and a campaign of so-called "massive resistance," where people at least in Virginia went as far as to close public schools and replace them with private to prevent integration.

Right at the tail end of your period, the Montgomery Bus Boycott started on December 1, 1955, when black civil rights activist Rosa Parks defied Montgomery's laws segregating their public busses and was arrested. The resulting boycott was led by a young minister new to Montgomery named Martin Luther King, Jr.