This chapter, which covers the first three decades of the twentieth century, begins with an account of the life and career of W. E. B. Du Bois, the most influential Black intellectual and social scientist of that period. A classic insider/outsider in American society, Du Bois earned a Harvard PhD in sociology and wrote a pioneering study of systemic racism in The Philadelphia Negro. He was also an outspoken activist in the Socialist Party and NAACP. Du Bois’s work placed him at the forefront of struggles against racism, especially in northern cities into which 1.5 million southern Blacks moved in the Great Migration, lured by the prospect of steady, well-paid factory jobs. These Black migrants, however, were outnumbered two to one by southern White migrants to those cities, who forced Blacks into ghettos with rundown, overcrowded housing and inferior schools. Tensions between the races intensified after World War I, sparking the “Red Summer” of 1919, with major race riots—instigated by Whites—in Washington, D.C., and Chicago, leaving dozens dead and thousand with burned-out homes. The bloodshed culminated that fall with the massacre of some two hundred Black tenant farmers and their families in the town of Elaine, Arkansas, followed two years later by another massacre, in Tulsa, Oklahoma. The decade of the 1920s offered northern Blacks little respite from the racism that kept them from escaping poverty.