In the actual international scenario, there has been a debate concerning the role of Japan in the Indo-Pacific. What measures will Japan enact to enter the region as a first-tier actor? Does Tokyo have a ‘grand strategy’ for the Indo-Pacific that goes beyond its borders? Michael Green presents ‘Line of Advantage’, an outstanding opera on Japanese grand strategy in the Indo-Pacific. In doing so, the author analyses the security architecture laid out thanks to the efforts of Shinzo Abe, who served his country between 2006 and 2020.

In chapter I, after introducing the history of modern Japanese grand strategy, Green highlights how nineteenth-century scholars and military strategists already realized that Japan's security lay on the sea, where a Navy should always be a maritime country's first line of defence. By underlining the critical importance of a naval strategy for the nation, using the British Empire as a model, the author provides a thorough historical narrative of the evolution of Japanese security strategy. The ‘line of advantage’ concept outlines the areas closely related to the safety of territorial sovereignty, which is more than the simple ‘line of sovereignty’ defining the national borders. But if the latter ones are clearly defined, apart from the disputed islands areas, the ‘line of advantage’ is a more flexible concept that depends on geopolitical variables from which no country can escape: from Malacca's dilemma to the chains of islands, even continental China is aware of the importance of maritime projection of a blue water navy to protect its national interests. As the author highlights, many security thinkers, from Tokugawa Nariaki to Fukuzawa Yukichi, always stressed the importance of emulating Great Britain's naval grand strategy and protecting Japan's safety and prosperity through maritime trade. Unfortunately, the political structure and the authoritarian regime that was in power at the time pulled Japan away from its alliance with Great Britain and closer to more continental policies until the Second World War. More recently, Japanese policymakers and security experts had to deal not only with the subordination of Japan to the United States under the Yoshida doctrine but also with the fact that Japan was de facto inserted into a security framework led by the United States, without a proactive role for Tokyo. As the author affirms, Japan shifted more recently from a ‘reluctant realism’ strategy to another, more assertive one, with the maritime element at its core and China's rising at its centre.

In chapter II, China is identified as Japan's main rival and one of the main reasons Japan needs an independent, proactive policy in the long term, even in case of the risk of American withdrawal from the region. However, China is also a strong economic partner, and Tokyo must find a way to balance cooperation and competition in its future choices. There is a strong belief of a minority in the liberal party, called ‘liberal institutionalists’, that Abe's maritime-focused approach would defuse conflict, as maritime security policies are usually centred on respecting and promoting universal norms and international law. On the other hand, Green considers the dangers of power transitions, i.e. a conflict arising when an emerging power is dissatisfied with the current status quo. Japan's new strategy shifted from hedging to resisting China's assertiveness through measures aimed at shaping Beijing's behaviour and containing its diplomatic, economic, and security expansion. Concerning engaging China multilaterally, it would have been convenient to have continuity in the book with regional institutions, which is later exposed in a different chapter. Instead, after introducing the leading actors shaping Japanese strategic choices, the author validly opted to discuss the core system of Japanese security architecture, i.e. the Japan–US alliance.

Chapter III deals with the United States, a core component of the Japanese security system. However, from Prime Minister Yoshida to Nakasone and from Kishi to Abe, there has always been an awareness of the necessity for a more independent policy, and the book highlights how the changing strategic environment contributed to strengthening the alliance. Nevertheless, the fear of abandonment or entrapment in a conflict Tokyo does not want may also play a part in the search for an alternative framework. The revision and upgrading of the 1997 guidelines of Japan–US defence cooperation in 2013 is the fruit of a long evolution of strategic thinking that opened to an extensive interpretation of Article 9, removing some obstacles that the Navy may face in answering a crisis. Overall, both American and Japanese security strategy documents highlight the importance of the Japan–US alliance. With the focus of the book being Japan's grand strategy and security interests under the Abe administration, it would have been useful to have a more omni-comprehensive approach that could take into consideration some Japanese strategic options in a case of conflict since there is a lot of debating ongoing on how to constrain China in the first chain of islands. A mention of ‘submarine diplomacy’, whose AD2A strategy is becoming increasingly important, could have given this chapter more analysis of Japanese strategic options.

Chapter IV takes a different direction and explores Japan's position in the Indo-Pacific. This guides the reader between the first part of the book, where the two main stakeholders are identified (China and the United States), and the Korean issue, and introduces a broader Japanese strategic approach. The author weighs the effect of each step the country made in its quest for a more proactive policy. The Indo-Pacific is also the scenario where Abe proposed elevating the ‘Quad’ talks (Japan, Australia, India, United States) to a more formal summit. The author introduces geopolitical concepts, such as Abe's ‘security diamond’ connecting Australia, India, Japan, and Hawaii, Spykman's ‘Rimland theory’, and the more recent ‘Free and Open Indo-Pacific’ strategy. This is one of the most critical passages in the book since this concept seems to be a point of reference not only for many European states that have drafted an Indo-Pacific strategy but also for Southeast Asian countries. This strategic framework allowed a maritime realignment of many nations, enhancing Tokyo's influence and creating a structure of priorities for Japan's security strategy.

Chapter V introduces Korea, and a contradiction emerges between the ideal commonality of strategic interests and geopolitical objectives, brought together by the shared alliance with the United States, and the impossibility of the two countries dealing with their historical heritage (comfort women issue and Japanese occupation), which still affects any attempt to create a solid partnership to engage security challenges more effectively. The diverging strategies in dealing with Beijing under an American-led strategy may jeopardize Japanese efforts to use international norms to contain China due to the history shared between China and Korea and their historical perception of Japan as an antagonist rather than an ally. Despite a commonality of strategic interests in the maritime field, Seoul perceives Japan as a revisionist country, even if an American hegemony is preferred to a Chinese one. The relationship between Japan and South Korea, which the author defines as dysfunctional, also plays a part in the failures in dealing with Pyongyang. It is worth mentioning that, according to some experts, the threat from North Korea should be a coagulant factor instead of a divisive one. Still, Korean internal politics created confusion and sometimes went against Japan and America on a diplomatic and maritime security level. The author decides to opt for a detailed analysis of the structural rivalry.

In the last chapter, the author, thanks to his experience with the Japanese Diet as an aid, gives an impressive overview of the evolution of the legislation that Japan produced in an attempt to offer its allies a model of trust to participate in initiatives such as ‘Five Eyes’ and other intelligence-sharing strategic options. On the internal balancing side, it is underlined how the domestic policies allowed increased defence expenditure by starting a modernization of the army, projecting its capabilities in faraway scenarios. Interestingly, he references the Quad framework and he is aware of the necessity of involving Southeast Asian countries. A geopolitical alignment of maritime powers and a more robust engagement with smaller states that may otherwise bandwagon with China are essential. In the debate between the qualitative internal balancing and the qualitative force of the military, reorganizing national security institutions is critical, but only with a reinforced economy and military power.

Overall, the book follows a structure that deals first with the history of Japanese strategic thinking. It considers its main ally and strategic rival. It regards the Indo-Pacific region as a whole, only to discuss later Korean and Japanese domestic security legislation. A chapter on geopolitical and strategic considerations would have engaged the reader, even the least informed ones, on a series of topics that would have given more depth to the central part of the book. Nonetheless, there is much more than an overview of the history of the Japanese internal legislative evolution: it shows that Japan is not and has never been a mere ‘reactive state’. The book does justice to Shinzo Abe's ‘Free and Open Indo-Pacific’ concept, which was not crafted in one day but rests on the shoulders of his predecessors, who contributed to the evolution of Japanese foreign policy strategy.

Line of Advantage sheds some light on Japanese grand strategy in the Indo-Pacific. However, the author's exhaustive overview of historical documents, interviews, facts, and events does not leave much space for engaging the existing realist literature in the field of realism in international security. Relevant authors are considered, such as Mike Mochizuki, Raja Mohan, and many more, but most of them are mentioned to support the author's point of view, or they stay in the footnotes. Green does not support the thesis that China could be ‘enmeshed’ in a maritime cooperative security framework. However, it could have been interesting to see this option being discussed. A stronger focus on Japanese maritime strategy towards Beijing and the new policies of other regional maritime countries could have given a more detailed shape to that Line of Advantage that seems to fall in the background, lost in the maze of historical information and political overview, and sometimes the geopolitical part does not get the reader's attention.

The author's background in international history, his experience in Japan as a staff member of the Diet, and his knowledge of the Japanese language and Japanese policymakers provides us with a unique internal perspective to understand where Japan is headed in the upcoming years of international competition. Overall, the book is an essential source of information for anyone interested in learning how Japan is dealing with the Chinese rise not only from an international perspective but also domestically: Japan is much more than an Asian ally of the United States, and Michael Green centres the objective in demonstrating it. One of the merits of this book is how Green supports Japan as a geopolitical actor that can move beyond its national boundaries to promote an independent ‘grand strategy’. Not so long ago, many think tanks and policymakers used to see Japan as a reactive country.

This is a book that anyone interested in Japanese security should read to understand how the country got to this point and how it will answer the current geopolitical challenges. It is a legacy to all those scholars and policymakers who would like to delve deeper into the dynamics shaping Japan to adopt a new strategic posture in the Indo-Pacific.