Those interested in history and IR theory, especially those with a constructivist bent, will find this book worth looking at, though it's not always easy going. The basic argument is that different dominant ideas about the "moral purpose of the state," coupled with different ideas about sovereignty and justice, give rise to very different forms of diplomacy and law in different eras. Most interesting, though not necessarily completely persuasive, is the distinction Reus-Smit draws between the "absolutist" and the modern European state systems, emphasizing the shift from "naturalist" to "contractual" international law, and from "old diplomacy" to multilateralism.