This work provides a "sociologically and anthropologically informed history" of the Somali people, spanning from their pre-colonial origins through the modern era. It examines the intricate interplay between the traditional clan system and the development of modern nationalism. The book was first published in 1965 and revised in 1980 and 1988 to include the history of the Somali revolution and the military regime.

Lewis details the Somali expansion from the north, the rise of medieval Muslim city-states, and the impact of the imperial partition of the nineteenth century. He provides an in-depth analysis of the holy war waged by Sayyid Muhammad 'Abdille Hassan and how his movement served as a forerunner to modern nationalism. The later chapters deal with the transition from trusteeship to independence and the subsequent political challenges.

The author utilizes both written records and oral traditional material to provide insight into the "cultural complexities" of Somali history. He argues that modern developments cannot be understood without appreciating the unique features of the Somali social system, which is characterized by an "unremitting struggle for power" and alliance.