What accounts for the unprecedented growth in human numbers during the past century? In what ways have race, nation, and ethnicity found expression and played a role in world history during the past century? What has caused such large-scale human movement to urban areas and other countries in the past century?

What accounts for the unprecedented growth in human numbers during the past century? In what ways have race, nation, and ethnicity found expression and played a role in world history during the past century? What has caused such large-scale human movement to urban areas and other countries in the past century?