THE 2000 census, on which the Census Bureau started issuing reports in March and April of 2001, reflected, in its structure and its results, the two enduring themes of American racial and ethnic diversity, present since the origins of American society in the English colonies of the Atlantic coast: first, the continued presence of what appears to be an almost permanent lower caste composed of the black race; and second, the ongoing process of immigration of races and peoples from all quarters of the globe, who seem, within a few generations, to merge into a common American people.