My quick summary of the book is this: Rosenberg seeks to find the foundations of a Marxist theory of international relations. He does this by going to the origin point of IR scholarship, the development of the realist theory of anarchy, and offering a thorough critique of that approach. To this end Rosenberg seeks to show the historical peculiarity of our international order. In particular, he seeks to draw out "the secret origins of the state" through a Woodian understanding of the Development of Capitalism.
I have seen other reviews of this book dismiss it as disappointing due its repetition of common Marxist talking points. While it is certainly true that the book goes over well trodden ground in terms of discussing Marx's theories, it is also true that it does so in order to build the foundations for an adequate Marxist approach to International Relations. As such, I think that critique is well taken but in the end flawed in its understanding of what the book has set out to do.
Chapter one is a thorough critique of the three key figures of Realist IR theory: Carr, Morgenthau, and Waltz. Each of them is given a short subsection which goes over their core theories and uses said overview to critique the naturalist approach to realism (for Morgenthau it is an assumption that states behave the way they do due to human nature and for Waltz it is a de-historicized concept of the Anarchy of the international system). This chapter is useful if you have an understanding of these scholars, as it uses their work to spring board into the core themes of the work. Without said understanding the chapter may be overly dense and confusing.
The next three chapters give a historic defense of the argument made in Chapter five, namely that we can only understand IR thorough an understanding of the history/societies from which it develops (and shapes... he is a bit too much with using the term dialectical in this regard). These chapters are fascinating, and especially elucidating if you have read either Brenner or Wood's work on the development of capitalism.
If you are simply looking to read the foundation's for Rosenberg's later work on Uneven and Combined Development/ International Historical Sociology, then this chapter is sufficient. It outlines Rosenberg's theory of Sovereignty (the growth of an impersonal public political power in the form of the state which is distinct from the extraction of surplus value) and his theory of anarchy (which he claims must be understood in relation to Marx's theory of the anarchy of production).
Overall, a good book, a fun read, and for someone formerly involved in studying IR, a good re-primer on the key arguments in the field.