In Fences, the major conflict is not between white and black, husband and wife, or old and young. Although all of these conflicts exist, the main conflict is between Troy and his internal and external "fences" (the limitations which keep him from achieving his dreams, opportunities, financial goals, interpersonal relationships, and self-image).
As a period piece about a working-class family in Jim Crow America, Fences pits the individual against personal (dreams), social (racism), economic (back-of-the-truck status), and institutional (church, military) limitations. Troy is drawn-and-quartered between all these limitations and, yet, he keeps getting burdened with more responsibilities within the family (more mouths to feed, his son's future, his brother's mental care, etc...). It's enough to make a man burst, literally and emotionally.
By the end of the play, Troy is dead and all of his family are "fenced off" in institutions: Gabe in the mental institution, Lyons in his music, Rose in the church, Cory in the military. Only Raynell, his illegitimate child, ironically, is not fenced off and burdened. She is Troy's legacy and symbolic of the next generation's hopes and dreams.