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 century's most pressing issues—such as climate change, economic inequality, political polarization, and security—are 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 (see Acuto 2013, 2021; Marchetti 2021; Van der Pluijm & Melissen 2007).

E-International Relations is free to read. We rely on reader support to make this possible.

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. The city of Yokohama especially 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). Yokohama’s 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 Yokohama’s 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). The City of Yokohama International Strategy, drafted in 2016 and revised in 2021, outlines the city’s 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 Yokohama’s 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 Yokohama’s 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 the C40 Cities in 2010 and even won an award in the Clean Energy category in 2016 for its Yokohama 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 city’s recognition as a UN Peace Messenger City, along with its activities through the Mayors for Peace organization, helps promote Yokohama’s 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 Yokohama’s diplomatic strategy is the........

© E-International