How did Hughes address the idea of race in America? How would you describe the overall tone of his work?
In addition to "solemn strength," one could also say that there is pride—pride in the "Negro's" resilience and permanence.
Hughes's narrator makes his or her experience as a black person central to history. Notice the use of anaphora, or repetition, in the poem: nearly every line begins with "I" or the contraction "I've." This is broken only twice with the phrase "my soul" and "ancient," which reinforce the narrator's place in history and his or her permanence given our understanding of the soul as something that never ceases to exist.
Hughes's approach to the poem reminds me of a statement that James Baldwin once made before an audience. It was along the lines of "One cannot enter the 21st-century without going through me first." This is to say that there is no moving forward without first acknowledging how we got there and how every historical event led us to this point. The assertion is that the history of America (and its future) is tied to the Black American experience, which is part of the origin story.
Hughes's narrator declares knowledge of an original world that existed even before human intervention: "I’ve known rivers ancient as the world and older than the flow of human blood in human veins." This narrator was a participant in the first civilization, signaled by his having "bathed in the Euphrates when dawns were young." However, this narrator has also known the Nile, the Congo, and, finally, the Mississippi.
The point here is that black people have always existed and have played a role in nearly every major civilization. This self-awareness—this knowledge of having always been here, of having always had a place in history—is the source of the narrator's pride and depth. It subverts the racist American narrative that insists that black people had no history and no real existence (an idea subverted by Hughes's constant use of action verbs) until white slavers took them from their homes.
The overall tone in the Hughes poem is one of solemn strength. The emotional connotation of the poem is that the description of the Black individual over history is one that has borne witness to the greatest of strengths, the most painful of moments, the most lofty of promises. The attitude implied by the word choice and feel of the poem is that there is a permanence in being Black and this level of constancy is what defines the Black person's strength. It is almost to say that the depth of the speaker's soul is a signal of strength, of commitment, of the ability to withstand all of what it means to be Black. In terms of how this poem speaks to race in America, there is a level of stoic resistance to all that African- Americans endure. While the challenges of racism and discrimination in American might prove overwhelming and challenging, Hughes seems to be saying in the poem that there is a level of strength and endurance in being Black. It envelops history and experience and through both, African- Americans will be able to place the challenges of race in America in a context where victimization will not result, but rather strength and triumph.