Which phrase describes the treatment blacks received in the years before world war ii?

Separate and unequal.

I suspect that's the phrase you're looking for, even if you haven't provided us with a list of phrase choices.   After the Civil War and prior to World War II, blacks in America had acquired a measure of civil rights, but they had not attained truly equal status with white Americans.  And many "Jim Crow" laws, as they were called, compelled blacks to stay separated from whites in society.