Most basic American history books point to a handful of big cases involving the rights of African-Americans.
There’s the Dred Scott decision. Voting rights established in the Constitution and the couple of Supreme Court cases where you can actually remember both sides: Plessy v. Ferguson (1896) and Brown v. Board of Education of Topeka, Kan. (1954).
Plessy v. Ferguson is commonly attributed as being the court case that established “separate but equal.” The latter, the Brown case, is supposed to have ended segregation entirely.
Of course, history is not as plain as that or as easy to enforce.