Because while the US was preaching for world peace and democracy through the world, US was a racially discriminatory, belligerent propagandist, suppressor of individual rights such as freedoms of thought and speech, in internal policies. A truly paradox. Du Bois first experienced southern racial prejudice as a student at Fisk University in Nashville, Tennessee. Later he was the first African American to earn degrees from Harvard (in history and sociology) and briefly attended the University of Berlin. Du Bois advocated that blacks should not be merely vocational but should develop bold leaders willing to challenge segregation and discrimination through political action.