Final answer:
Frederick Douglass identified prejudices, historical injustices, and the perpetuation of white supremacy as the core causes of racial discrimination in the U.S. He worked towards a diverse 'composite nation' but faced opposition, notably in the fight for naturalization and voting rights for nonwhite groups.
Step-by-step explanation:
According to Frederick Douglass, a prominent African American leader, the grand cause of racial discrimination in the United States was deeply rooted in prejudices, historical injustices, and a social order that sought to perpetuate white supremacy.
Douglass, alongside other civil rights activists, fought against the discrimination of not only African Americans but also other nonwhite groups such as Chinese immigrants, Native Americans, and non-Christian faiths. Discrimination persisted post-slavery through institutionalized racism, barriers to citizenship for nonwhites, and defacto segregation in the North, despite it being less overt than in the South.
In his advocacy, Douglass envisioned America as a composite nation that would embrace diversity and provide equal opportunities regardless of race. The challenges in realizing this vision were evident through the segregation and discriminatory laws like the Jim Crow laws, and the exclusionary naturalization statutes.
Douglass, and others like Charles Sumner, called for inclusion in the national fabric, but were met with strong resistance, particularly in matters regarding naturalization and the suffrage movement.