What is the main conflict in Ethnic America: A History by Thomas Sowell?

Ethnic America, written by economist and historian Thomas Sowell, is a history of nine ethnic groups that immigrate to the United States. Sowell's aim is to illustrate important points about history, economics, social science, social philosophy and social policy in these histories in order to draw certain lessons towards the end of the book. Yet the histories are of great interest in themselves, as they tell the human story of the profound struggles and impressive achievements of the individuals within these groups.