A specialist in the history of Ireland and the British Commonwealth, Philip Nicholas Seton Mansergh was the Smuts Professor of Commonwealth History at Cambridge University from 1953 until 1970.
Nicholas Mansergh provides an excellent overview of how the British Commonwealth came into formation starting with the Durham Report. Mansergh carefully explores the internal British debates on what direction the empire should take along with how the Dominion states were assessing their role in world affairs. The book culminates with the Anglo-Irish treaty and the start of the formal commonwealth as most historians recognize it. There is a follow up volume that takes the reader through the rest of the history of the commonwealth but this one stops with the formation. Overall it is easy to read and a great look at how the commonwealth was formed.