Over the last two decades, American policymakers have increasingly used sanctions to punish countries that transgress U.S. and international norms, or attack U.S. interests. Sometimes these sanctions are coordinated with multilateral sanctions; sometimes the U.S. applies them alone. Sometimes the U.S. puts forward comprehensive sanctions against a country; sometimes it only sanctions particular companies or organizations in a country rather than the country itself. In some cases, the U.S. continually adjusts its sanctions against a particular country; in other cases, those sanctions remain fairly static.
The variety of sanction packages begs a question: which ones actually work in changing the behavior of the state being sanctioned? Part of the surprising multifaceted answer to this question, according to Meghan O' Sullivan, is that many policymakers don't even seem to care. Instead, they look upon sanctions as a generic expression of disapproval against the country being sanctioned -- with U.S. domestic interests often affecting the actual shape that disapproval takes -- rather than as a practical tool of statecraft.
O'Sullivan's book is an attempt to rescue sanctions from this current state by showing their potential as effective policy to change the sanctioned state's behavior. She does this by closely examining four case studies where the U.S. employed sanctions against countries it deemed to be state sponsors of terrorism - Iran, Iraq, Libya, and Sudan.

This book's twin cardinal virtues are its thoroughness and its cautious conclusions. Despite footnoting every twist and turn in how the U.S. employed sanctions in the four cases, and what subsequently happened in those sanctioned countries, O'Sullivan never overreaches in her claims. Many places in the book, she is careful to note that proving what sanctions accomplished (or did not accomplish) in any particular case is extremely difficult to separate from other factors affecting the outcome. Nevertheless, she superbly teases out some interesting and valuable conclusions from the data.
At the end of her book, O'Sullivan focuses on what policymakers need to do to make sanctions effective policy rather than just dramatic policy. She believes they should employ sanctions that are flexible, as well as maintain open channels of communication with the sanctioned country. Too often, U.S. policymakers have used rigid and redundant guidelines for sanctions that don't allow the target to be rewarded for good behavior. Without this flexibility, there is almost no incentive for the country to change. This causes the U.S. sanctions regime against it to harden into permanent U.S. policy, even when there is little interest in either country for this to happen.