“It was the shared claim of whiteness, not language or custom or heritage, that allowed Dutchmen, Irishmen, Germans, Frenchmen and Swedes to come together with Englishmen and Scots as fellow Americans. Whiteness was the basis of commonality in the formation of the American common man. It conferred entitlement to manufacturing jobs and commercial opportunities in the north and to land in the west. Practical applications of the doctrine of white supremacy went far beyond southern defenses of slavery. Northerners also drew on the doctrine in their arguments for keeping or driving blacks out of their communities.”