How were blacks treated in 1948-1973 in the southern United States?
What you have to realize here is that this covers a great deal of time in which conditions changed tremendously for African Americans.
At the beginning of this time, segregation was in effect all over the South. Southern states used various legal devices to prevent African Americans from voting. There was still a fair amount of violence against African Americans who (like Emmet Till) stepped out of the role that was expected of them.
By the end of this time period, African Americans had gained legal equality. The 1964 Civil Rights Act and the 1965 Voting Rights Act had put an end to segregation and legalized discrimination. Of course, racism still existed (as it still exists today). But African Americans were treated equally in terms of the law by the end of this time period.