One of the problems in a country divided by racism, especially one in which racial segregation is a component of the national culture, is the arbitrary marginalization of talent simply because of a benign trait like skin color. One can only speculate how different the history of Major League Baseball would have been had players like Satchel Paige and Josh Gibson been permitted to participate. Or, how different the arts and sciences would have been had talented, qualified individuals not been excluded because of their ethnicity.
When discussing the contributions of the Harlem Renaissance to American culture, one should think in terms of wasted opportunities because of systemic racism. A century after the Emancipation Proclamation, African-Americans were still struggling for basic civil rights. Living under the oppressive boot of segregation, African-Americans developed their own forms of art and literature.
Perhaps nowhere was the contribution of the culture that developed in Harlem more pronounced than in music. The history of jazz begins in Harlem. Black communities in other cities, for example, Kansas City, were developing their own forms of jazz, but it was in Harlem during the 1920s that the form really took off. Duke Ellington could be considered the father of jazz, but he was not alone, as Fats Waller and others developed their art form in Harlem during that period. To this day, jazz is considered America's greatest cultural contribution to the world. Its influence on the broader American culture is found in the myriad Caucasian songwriters and musicians who claim to have been heavily influenced by jazz musicians.
The contributions of the Harlem Renaissance to American culture extends also to the areas of literature and poetry, personafied by the work of Langston Hughes and Zora Neale Huston.
These artists found followings in White America that helped Blacks to cross the cultural divide and gain acceptance in much of the country. The systemic racism would continue for several more decades, but the cultural contributions of the Harlem Renaissance are a fact.