Like the poem, the answer to this question is a complex one.  The poem succeeds in its attempt to have American society acknowledge African- Americans as owners of a culture given to the nation.  In being able to link the current experiences of African- Americans to a rich and vibrant history, Hughes is able to suggest that there is a long and profound cultural narrative which defines what it means to be African- American.  The fact that Hughes argues African- Americans have known "rivers ancient as the world and older than the flow of human blood in human veins" helps to convey this.  It brings forth the idea that American society has not been around as the contribution of the African.  Hughes's detailing of the history of his people, the people of color, reflects this.  While the condition of racism and slavery might be a part of their culture in America, Hughes is able to bring out a historical condition in which African- Americans own a culture that they have bequeaths to the United States, a nation that is relatively young in comparison to the deep and profound roots in cultural identity that Africans hold.

However, it is in this reality in which Hughes's poem critiques the notion of what it means to be "fully enfranchises American citizens."  Hughes argues that the deep and profound history that African- Americans hold is one that transcends the current challenges they face in America.  The reality is that Hughes's poem illuminates how that the history of Black people will go on, despite the fact that they are not fully enfranchised American citizens.  The poem succeeds in being able to evoke a condition where it is evident that people of color are not treated as fully enfranchised American citizens.  Theirs is a history that moves beyond the contingent and the temporal.  The poem brings out the injustice intrinsic to the denial of a full enfranchisement as American citizens.  While the poem cannot secure full enfranchisement because America has failed to secure full enfranchisement for African- Americans, the poem brings forth a reality that such a denial is unjust and unfair.  The poem succeeds in illuminating the history of Black people, one that transcends even the history of America.