What happens when local governments that cannot make treaties enter into written commitments with foreign governments? Japan offers a striking example. Its prefectural governments have concluded a substantial number of such commitments, covering economic cooperation, tourism, disaster management, agriculture, and environmental protection, education, research, sports, and even coordination with the US military. Yet until recently, their overall scale and legal character were largely unknown.
These agreements matter because they challenge a familiar picture of international relations. We usually imagine that sovereign states conduct diplomacy and make international agreements, while subnational governments remain within national borders. Japan’s experience suggests a more nuanced picture: subnational governments can become meaningful international actors without possessing treaty-making power or conducting diplomacy separate from the national government.
My interest in this subject began with my work in international law and US foreign relations law. The US Constitution prohibits individual states from entering into treaties and limits their ability to conclude agreements or compacts with foreign governments. Nevertheless, US states have entered into a remarkable number of international commitments. These arrangements address matters such as trade and investment, cooperation in general terms, environmental and natural resources, transportation, and education.
These agreements matter because they challenge a familiar picture of international relations.
How can subnational governments engage internationally when constitutional law denies them an independent treaty-making power? In recent years, scholars have increasingly examined the international activities of states, provinces, regions, and cities under the concept of paradiplomacy. Subnational governments now cooperate across borders on issues that directly affect their residents, including climate change, public health, disaster response, tourism, investment, and local economic development.
Much of this literature, however, focuses on federal systems and on North America and Europe. Unitary states such as Japan receive less attention. This gap in the literature made Japan an especially interesting case: How, and to what extent, were its prefectural governments engaging internationally?
The first surprise was how little anyone seemed to know. Japanese scholars have long recognized that prefectural governments engage in a wide range of international exchanges and issue public statements on security issues. Information on sister-city and other friendly relations has also long been collected in Japan. But no comprehensive record existed of prefectural commitments concerning other fields, such as economic cooperation, human resources, disaster response, agriculture, or scientific research.
The Ministry of Foreign Affairs and the Ministry of Internal Affairs and Communications do not maintain a complete list. No national database shows how many such agreements exist, what subjects they cover, or what legal effects they are intended to produce.
To answer these questions, I sent information disclosure requests to all forty-seven prefectural governments across Japan. Some relevant documents were already publicly available, but many were not easy to identify. My research ultimately identified approximately 180 written commitments concluded by Japanese prefectures with foreign governments or governmental entities between 1983 and 2025.
The real lesson was not that prefectures had acquired treaty-making authority, but that international cooperation can be achieved through different kinds of international agreements with different legal effects.
At the outset, it seemed possible that the collected documents would reveal a constitutional problem. If Japan’s Constitution gives authority over foreign affairs and treaty-making to the national government, were some prefectures acting ultra vires—that is, beyond their lawful authority?
Rather than conflicting with Japan’s foreign policy, these arrangements generally operate in support of it.
The collected agreements point in a different direction. Looking across the prefectural commitments, little evidence suggests that prefectures were attempting to conduct an independent foreign policy or challenge the national government’s diplomatic authority. Nor was there any broader pattern of litigation, diplomatic disputes, or serious negative consequences arising from these agreements. Instead, the documents revealed a largely practical and constructive network of international relationships, especially with Asian countries, such as Thailand and Vietnam. Rather than conflicting with Japan’s foreign policy, these arrangements generally operate in support of it.
Not every written agreement between governments is a treaty. International practice includes several types of commitments with different legal effects. Treaties create rights and obligations governed by international law. Contracts may create enforceable rights or binding obligations under domestic law. Non-binding political commitments establish expectations and frameworks for cooperation without creating legally enforceable duties.
Most of the prefectural agreements examined fall into the third category. Many expressly state that they are not legally binding. Others use broad, non-mandatory language concerning cooperation, encouragement, promotion, efforts, or future exchanges. A smaller number contains more specific reciprocal responsibilities, such as how travel, accommodation, or transportation expenses are allocated between the parties. Others require the exchange of personnel, the provision of materials, or the implementation of particular projects. These arrangements are better understood as contracts governed by domestic law rather than as treaties governed by international law.
Once these distinctions became clear, the apparent constitutional problem became much less serious. Japan’s prefectures are not exercising formal treaty-making power. They are using different legal and political instruments to carry out ordinary local responsibilities in an increasingly international environment. Japanese law does not expressly grant local public entities the authority to engage in international activities. Instead, the law broadly assigns them responsibility for the autonomous and comprehensive administration of local affairs. The breadth of this grant of authority enables local public entities to engage in international activities that are closely connected to residents’ daily lives and promote their welfare. Promoting local industries, preparing for disasters, encouraging tourism, and protecting public health remain local governmental functions even when cooperation with a foreign partner is necessary. These activities ultimately serve the interests of local communities and their residents.
Agreements involving United States Forces Japan, which is the US military command in Japan, provide a particularly useful example. Some prefectures, including Tokyo and Okinawa, have concluded arrangements concerning disaster response, humanitarian assistance, or emergency access to facilities. At first glance, agreements involving foreign military forces may appear especially sensitive. Yet these arrangements operate within the broader framework established by the Japan-US Security Treaty and the Japan-US Joint Committee, which is a bilateral consultation body under the Status of Forces Agreement. They implement treaties ratified by Japan and national policy, helping local governments respond to practical needs within the national legal and diplomatic framework.
The documents ultimately revealed that my initial question was the wrong one. The issue was not whether prefectures had somehow acquired treaty-making authority, but how they had developed alternative forms of international commitment that enabled them to build cooperative relationships without exercising treaty-making authority.
Beyond Japan, many constitutional systems reserve foreign affairs to the national government. At the same time, globalization increasingly requires local governments to cooperate across borders. Climate change, infectious disease, natural disasters, economic development, and environmental protection often transcend national borders and the traditional allocation of responsibilities between national and subnational governments. This can appear to create a choice between constitutional principle and practical necessity.
Subnational governments do not need treaty-making power to develop meaningful international partnerships.
The example of Japan suggests that this is a false dichotomy. Subnational governments do not need treaty-making power to develop meaningful international partnerships. They can rely on non-binding political commitments and contracts suited to the functions they actually perform. Even where commitments are expressly non-binding, they are generally observed in practice. Japan’s experience demonstrates that constitutional limits on treaty-making need not prevent subnational governments from building durable international partnerships.
Japan’s prefectural agreements reflect the thickening of international relationships below the national level. In this respect, Japan’s experience is consistent with a broader trend identified in the paradiplomacy literature: subnational governments increasingly contribute to the development of international relationships through practical cross-border engagement.
Japan, however, also offers an additional lesson. These relationships have developed without conferring treaty-making power on prefectures or undermining the constitutional allocation of authority over foreign affairs. International engagement is therefore no longer conducted solely through treaties, embassies, and national ministries. It is also built through sustained, practical interactions among local officials, public institutions, and communities.
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Yuhei Matsuyama is a tenured, full-time lecturer in the Faculty of Law at Fukuoka University in Japan, specializing in international law and US foreign relations law.
Suggested Citation:
Yuhei Matsuyama, “What Japan’s Prefectures Can Teach Us About International Engagement by Subnational Governments” USALI Perspectives, 7, No. 2, September 15, 2026, https://usali.org/usali-perspectives-blog/what-japans-prefectures-can-teach-us-about-international-engagement.
The views expressed in USALI Perspectives are those of the authors, and do not represent those of USALI or NYU.
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