Why is the phrase "five score years ago" more appropriate than "a hundred years ago" or in "1863" why does king later repeat the phrase "one hundred years later" so often?

Five Score Years Ago Is more appropriate because it is another way of saying 100 years ago and 1863.He repeats one hundred years later to let you know that this is after four score years ago.

It developed as a reaction to the impact of european colonialism in africa on peoples of african descent. in the  mid-20th century, activists in africa adopted pan-africanism as a rallying cry for independence from colonial rule. some african pan-africanists sought to unite the continent as one independenthope it was useful