Who enforced segregation of black and whites in public places?

Answer 1

You are referring to "segregation." After President Lincoln freed the slaves, many southerners were bitterly unhappy about it. Their solution was racial segregation, a system rooted in racism and based on a misreading of Scripture which claimed that black people had been cursed (The Bible says no such thing) and that blacks and whites were supposed to be separate. In the south, segregation was "de jure" (by law) whereas in other parts of the United States, it was "de facto" (by custom), but in both cases, the end result was that black students attended inferior schools (many of which had no college preparatory courses); often were forced to live in inferior neighborhoods; and in the south, were forbidden from attending good colleges or seeking careers in certain occupations.

Up north, where black students did attend schools with white students, some were able to get into college and achieve, but the popular culture continued to reinforce the idea that white people were superior, and even in integrated schools, expectations for black students were often quite low. Segregation ended with the Supreme Court's 1954 "Brown vs. Board of Education" ruling, but the attitude that racial separation was necessary and desirable persisted amongst many white southerners well into the 1960s and 1970s.