The civil rights movement of the 1960s spurred a generational and cultural discontinuity in the Black community parallel to that among whites. In both instances, Republicans were on the side of tradition, order, and more gradual progress, and opposing street protests against the Viet Nam war and disorderly mass civil rights protest marches.
In both instances, the new cultural and political loyalties among the young who embraced such protests accrued to the enduring benefit of the Democrats and the Left. A new generational shift will soon be underway though when young people realize that they have been handed the bill for their elders' unsustainable Medicare and Social Security benefits, with a future further constrained by a dismal regulatory and tax structure fashioned by the Left.
Definitely, there is validity to that explanation, as well.