In this book, Diamond seeks to explain that racial inequalities are not caused by race. Race, therefore, does not play any role in causing the inequalities that are observed among people of different races.
As Diamond answers Yali's question, he emphasizes that race is not important. Societies did not become strong or weak because of their cultures or because of the race of their people. Instead, their fates were determined largely by their geographic luck.
Therefore, Diamond would say that racial inequality came about because white people were lucky enough to arise on a continent where it was easy for farming to arise and spread. Africans, Native Americans, and other non-whites were less lucky because they did not live on such a continent.