Daniel Clausen

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Feb 20 2026

It has become commonplace to think of the 21st century as the urban century (Carnegie Endowment for International Peace 2023). With roughly 70% of the population estimated to be living in cities by 2050 (United Nations, Department of Economic and Social Affairs 2018), it is becoming increasingly apparent that many of the 21st centurys most pressing issuessuch as climate change, economic inequality, political polarization, and securityare intertwined with city politics. In the backdrop of both intensifying global problems and growing economic and political power, cities and other subnational groups have been stepping up their global activity, attempting to fill in gaps in global governance and advocacy.The growing efforts of cities and other subnational groups on the international stage have been termed city diplomacy, as well as urban diplomacy, local diplomacy, and subnational diplomacy; the practical applications of city diplomacy include the activism of mayors and city officials, sister city relationships, the hosting of international events, and participating in city networks, to name but a few (seeAcuto 2013,2021;Marchetti 2021;Van der Pluijm & Melissen 2007).

In the early 2010s, Michelle Acuto (2013, 1-3) could reasonably claim that cities were the invisible gorilla in global politics: highly impactful entities that were ignored by a scholarly community overly focused on states. However, since Acuto gave recognition to the invisible gorilla, a burgeoning subfield has emerged that has expanded our understanding of city activities on the global stage. This scholarship has grown hand in hand with the actual maturity of city diplomacy. With the evolution of this subfield, we now have a deeper understanding of the capacity of cities to act in terms of their financial resources, administrative organization, and training (Kosovac et al. 2020); the growing role of city networks in addressing global issues (Acuto 2013, 2021; Marchetti 2021, 78-81;Miyazaki 2021); the attractive soft power of cities (Grincheva 2020; Marchetti 2021, 82-84); and the continuing relevance of sister city connections (De Villiers, Smit, & De Coning 2007).

For this article, Yokohama and Taipei have been selected to illustrate diverse applications of successful or proactive city diplomacy. By comparing aspects of these cities, the essay hopes to uncover insights that could enhance the practice of city diplomacy and contribute to the expanding body of literature seeking to professionalize this field (for example,Meridian International Center 2025).

The City Diplomacy of Yokohama

The city of Yokohama resides just south of Tokyo, facing Tokyo Bay. As a port city with more than 3.5 million residents, it is the second most populous city in Japan and is part of a larger urban area that includes Tokyo. Thecity of Yokohamaespecially began to flourish as a port city for international trade following the opening of Japan during the Meiji Restoration in the mid-19th century (Encyclopedia Britannica 2025b). Yokohamas approach to city diplomacy includes technical cooperation between cities, activism on global issues such as climate change, peace, and development, as well as sister city relationships.

A significant aspect of Yokohamas approach to city diplomacy is its use of a publicly available International Strategy pamphlet, which highlights past activities and sets broad themes for its approach to global outreach (City of Yokohama, International Affairs Bureau 2021). TheCity of Yokohama International Strategy, drafted in 2016 and revised in 2021, outlines the citys plan to enhance its global engagement. The document outlines three objectives: foster an inclusive society and empower the next generation to bridge cities and people; engage dynamic foreign organizations and individuals to grow Yokohamas economy; and enhance cooperation to address global issues and promote peace and prosperity (City of Yokohama, International Affairs Bureau 2021, 4). Much of the short strategy pamphlet represents aspirational language that is useful for public relations. However, its very existence points to professionalism on the part of the city and its willingness to create a common blueprint for international and domestic partners.

An important pillar of Yokohamas diplomatic strategy is its participation in city networks and international organizations. Its activities through these organizations promote its agenda in peacebuilding, sustainability, and climate change. For example, Yokohama became a member of theC40 Citiesin 2010 and even won an award in the Clean Energy category in 2016 for itsYokohama Smart City Project (YSCP), a smart-energy and decarbonization project enacted in cooperation with 34 major Japanese companies (City of Yokohama 2020; City of Yokohama, International Affairs Bureau 2021). Additionally, the citys recognition as a UN Peace Messenger City, along with its activities through the Mayors for Peace organization, helps promoteYokohamas peace-making aspirations(City of Yokohama 2019). Other notable activities include its participation in ICLEI Local Government for Sustainability, the Carbon Neutral Cities Alliance, and the SDGs Leadership City Network (City of Yokohama 2020; City of Yokohama, International Affairs Bureau 2021).

Another key pillar to Yokohamas diplomatic strategy is the promotion of its expertise in urban development. Initiated in 2011, theY-PortProgram is a public-private partnership that brings together Yokohama city officials, local civic organizations, partner cities, and international entities to help solve environmental problems related to urban development throughout Asia. The programs supporters include major Japanese companies such as JGC Corporation and Chiyoda Corporation; partner cities like Batam City, Indonesia, and Cebu City, Philippines; and key international organizations such as the Asian Development Bank (ADB), to name just a few. Examples of projects undertaken through this project include improving water and sanitation conditions in Metro Cebu, Philippines; advancing Japans autonomous driving technology in Thailand; and assisting with solar power generation installation and management in parts of Thailand (City of Yokohama n.d.; City of Yokohama 2018).

Yokohama haseight sister cities and seven partner citiesin total, many of which were formed in a roughly twenty-year span from 1957 to 1977 (City of Yokohama 2025). Like other cities throughout the world, Yokohama focused on cities with shared attributes; in the case of Yokohama, fellow port cities. The importance of Yokohamas sister city relationships can be witnessed in its support for Odesa, Ukraine. In March 2023, the mayor of Odesa visited Yokohama to thank the city for its support during the Russian invasion of Ukraine. During the visit, the two cities promised to deepen collaboration on post-war reconstruction, culminating in the signing of aMemorandum of Understandingon sustainable urban development. Since the war began, Yokohama has committed to providing humanitarian aid, technical cooperation, and help with rebuilding critical infrastructure (City of Yokohama Global Offices 2023; United Nations Development Programme 2023).

The City Diplomacy of Taipei

The city ofTaipeiis another instructive example of city diplomacy. Taipei is the capital and political center of Taiwan (Republic of China) and home to over 2.5 million residents (Encyclopedia Britannica 2025a). One key function of Taipeis approach to city diplomacy is toovercome Taiwans political isolation(see Ferenczy 2020; Newland 2023). This motivation is often apparent inthe activism of Taipeis mayorin international forums and conferences around the world (see, for example, Taipei City Government 2025a). Through its many efforts, whether it is promoting its cultural heritage, demonstrating its expertise on sustainable development and smart city technology, or expanding its sister city connections, one can see a city that is striving to gain global recognition.

Taipeis involvement in city networks and international organizations is an important aspect of its global diplomacy. The city is a member of the United Cities and Local Governments, Asia-Pacific Branch (UCLG-ASPAC), where it holds an executive position (Taipei City Government 2024). Though not a member of C40 Cities, it has still won recognition for its efforts on environmental issues, garnering theC40 Cities Citizens Choice Award in 2014(Brittlebank 2014). Other notable activities include Taipeis participation inSister Cities International, CITYNET, the Asia Pacific Cities Summit, and the World Cities Summit, to name just a few (Taipei City Government 2024). In various ways, these organizations help to expand Taipeis presence on the global stage and promote dialogue on important issues such as smart-city technologies. On the issue of smart-city technologies, Taipeis global impact is significant. Taipeis contributions include hosting theSmart City Summit & Expo (SCSE)and the creation of theGlobal Organization of Smart Cities (GO SMART), which boasts more than 2,000 members worldwide (Smart City Online n.d.; Taipei City Government 2023).

TheSongshan Cultural and Creative Parkis another important element in Taipeis global engagement. The facility, which was a former tobacco factory, was repurposed in 2011 and now serves as a showcase and incubator for creative industries. The park has hosted important design events, including the Golden Pin Design Award, Red Dot Design Award exhibitions, and Creative Expo Taiwan. Additionally, it operates the Taiwan Design Museum and runs international student ambassador programs. As a creative hub, the Songshan Cultural and Creative Park demonstrates the importance of urban spaces as attractive soft power (Chiu & Spinney 2024; Taipei City Government Cultural Affairs Bureau n.d.).

Taipei has53 sister cities, 3 partner cities, and 5 friendship citiesworldwide, with agreements formalized between 1961 and 2024. The geographical diversity of these relationships is quite impressive, with the first sister city relationship being with Houston, US, in 1961 and the latest being Basseterre, Federation of Saint Christopher and Nevis, in 2025 (Taipei City Government 2025b). Beyond the usual rationales of education and cultural exchanges, business investments, and sharing urban development know-how, these relationships allow Taipei to improve Taiwans visibility on the global stage.

Maturing City Diplomacy Case-by-Case

There is a growing trend toward the professionalization of city diplomacy and the spread of best practices. We see this especially in the efforts of organizations such asC40s Knowledge Hub,the City Diplomacy Lab, and theMelbourne Centre for Cities, to name just a few, working to improve city diplomacy practices. We also see this in the growing number ofacademic publications devoted to city diplomacy. This literature has grown little-by-little often by understanding the specific cases of cities, particularly the successes of each city.

Both Yokohama and Taipei are important cases because they demonstrate a maturing approach to city diplomacy. These two cities share a strong emphasis on sustainable urban development and technology, especially smart city systems. Yokohama demonstrates its technical expertise through initiatives like the Y-Port Center, which has been a platform for its expertise on water and waste management and other urban development services. Taipei is also keen to share its technical expertise through participation in international conferences and events. Both cities are also participants in important global city networks with a focus on combating climate change and urban pollution. However, there are also important differences. Taipei seeks to use its city diplomacy to enhance legitimacy and visibility on the international stage, emphasizing cultural exchanges and sister city partnerships, whereas Yokohama seeks to lead on expertise-driven urban development that utilizes public-private partnerships.

Together, Yokohama and Taipei illustrate two distinct but complementary models of city diplomacy: one driven by technical cooperation and development expertise, the other by soft power and political visibility. Their approaches reveal how cities can act as vibrant international actorsadvancing local interests, strengthening global ties, and shaping international discourse from the municipal level.

As the 21st century advances, we can expect examples like Yokohama and Taipei to become even more important. City diplomacy, as well as other examples of subnational diplomacy, is becoming increasingly vital as state-level diplomacy becomes acrimonious, brittle, and subject to the whims of individual leaders (for a discussion, seeEconomist 2025). We see these adaptations increasingly in headlines that show subnational actors working around international deficiencies and deadlocks, for example, in the decision ofNew York (as well as the states of California and Illinois) to join the WHOs Global Outbreak Alert and Response Network (GOARN)in the aftermath of the USs withdrawal from the WHO (Singh 2026). These types of adaptations to the shortcomings of state-level diplomacy provide hope to those who believe the solutions to 21st-century problems lie in more global cooperation, not less. Thus, city diplomacy, though important, perhaps should be considered part of a larger story of global political activism below, around, and beyond state diplomacy that is working actively to cover gaps in global problem-solving. Though not a complete panacea to the deficiencies of state-level diplomacy, the efforts of citiesand other global actorsshould at least be seen as cause for cautious hope.

This paper was developed from a short essaypublished in Global Policy Onlineon August 1, 2025.

Table 1

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Further Reading on E-International Relations

• City Diplomacy: The Case for Eclectic (and Humble) Theorizing
• Opinion Beijings Weaponisation of Diplomacy Against Taiwan
• Dashing Lines and Faking History: The Complicated History of Taipeis Maritime Claims
• The Art of Diplomacy: Museums and Soft Power
• Sino-Taiwan Chequebook Diplomacy in the Pacific
• Kathmandu: City of Peace, Economies of Scale and Cultural Diversity

About The Author(s)

Daniel Clausenis an Associate Professor at Nagasaki University of Foreign Studies. His research has been published in Asian Politics and Policy, Electronic Journal of Contemporary Japanese Studies, and East Asia Forum, among other publications. He has also written several novels and short story collections. You can learn more about his work on his Amazon pagehereor on his Goodreads pagehere.

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