questioningmyreligion

If We believe that men will be punished for their own sins, and not for Adam's transgression. and slavery was abolished in 1865 and blacks were allowed to vote in 1965 How come blacks were finally allowed the Priesthood in 1978? So all black people were punished for Cain's transgression in regards to the Priesthood just because of the color of their skin? I know the first two examples of progress refer to the US and not the Mormons, but why were they so slow in furthering equality?