Wavering Alliances and Remaining Bases:


Considering the “Sphere of Influence”


During the Trump Era

By KAWANA Shinji

1. The US Overseas Base Network and Its Characteristics

In 2025, the United States had 549 overseas bases in 45 countries; about 20% of all countries have accepted US military bases. By military branch, 229 are Army bases, 122 are Navy, 181 are Air Force, and 31 are Marine Corps facilities. Marine Corps bases have been established only in Japan and South Korea, and most of these are in Okinawa. In terms of the number of facilities, Japan, with 98, is second only to Germany, where they were increased in light of the Ukrainian war. However, in terms of base area, it is the largest in the world.

It is necessary to distinguish the overseas deployment of the US military into bases (hard) and personnel (soft). In other words, although President Trump announced a decrease in their deployment to Germany recently, the implications differ depending on whether that refers to a reduction in the bases themselves or to the number of stationed American troops. Over the past 70 years, approximately 30 countries have hosted US bases, with few major changes. Nevertheless, the number of troops stationed overseas has changed significantly, influenced by the armed conflicts involving the US, such as the Korean and Vietnam Wars. In recent years, access rights and joint use have become more important than fixed and large-scale bases, but the base network itself has a high degree of continuity.

2. Base Endurance: “Troops leave, but bases remain”

Overseas deployment of the US military is characterized by “troops leave, but bases remain.” Among the bases are “light bases” centered on access, located in the Philippines, Singapore, and Latin America, and “heavy bases” with exclusive bases, administrative rights, their own assets, and various systems, located in Japan and South Korea.

Particularly heavy bases have high sustainability stemming from years of investment, institutionalization, aggregate effect, learning effect, etc. Even if returned, they are often converted into a Self-Defense Force facility and maintain their function as a joint-use base; bases do not simply cease to exist. Hence, changes in military configuration and the continuation of a base do not necessarily coincide, and bases are said to have their own endurance.

3. Setback in the Okinawa Marine Withdrawal Plan and Base Restructuring

One case demonstrating the endurance of bases is the plan considered between 1968 and 1969 for the withdrawal of marines from Okinawa. At the time, the US Department of Defense had formulated a large-scale reorganization of bases: consolidation of the aviation functions in Yokota, closure of Sasebo, concentration of home port functions to Yokosuka, closure of the Futenma air base, and withdrawal of the Marine Corps stationed in Okinawa.

This plan was formulated against the backdrop of a strategic decision to reduce the required Marines stationed after the Vietnam War, a reduction of the financial burden, and political considerations, preparing for the restoration of Okinawa. However, the plan was later abandoned because of strong military opposition, including from the Pacific Command (PACOM) and the Joint Chiefs of Staff (JCS). Instead, Okinawa was positioned as a core base for the forward deployment strategy in the Western Pacific, and its functions were strengthened as a base for the deployment of the 3rd Marine Division and the 1st Marine Aircraft Wing. Consequently, the basic structure of the Marine Corps in Okinawa, as it exists today, was formed.

4. The International Order and Sphere of Influence from the Perspective of the Base

The issue of bases does not concern only the placement of military installations; it is deeply linked to the international order itself. The State Department’s approach of prioritizing the borders according to international law and the military’s approach of prioritizing them according to security do not necessarily coincide, and the military has traditionally placed more emphasis on the sphere of influence as a strategic space than on the borders of sovereign states. From this perspective, the current Trump administration’s approach can find continuity with the sphere of influence idea envisioned by the military in the early postwar period.

The US military base plan (JCS570/2) formulated at the end of World War II regarded the Western Hemisphere and the Pacific Ocean as an integrated “American Zone,” assuming a division based on the spheres of influence of the “four policemen”—the US, Britain, the Soviet Union, and China—and assuming that the surrounding area would be defended by a “chain of bases.” This concept did not include Europe and the Middle East within the original US sphere of influence, and the Western Hemisphere and the Pacific Ocean were recognized as the core strategic space of the US.

5. Analysis and Outlook: Where are the Issues Shifting?

However, when the premise of the division of spheres of influence collapsed after the war, the US turned to building a global base system, which included Europe and the Middle East. In JCS 570/40 of 1945, a forward-deployed base network was envisaged as a “cushion of distance” for the defense of the mainland.

However, securing overseas bases was not easy. Countries hosting bases have concerns about sovereignty violations and being drawn into conflicts, and negotiations regarding military bases have often been difficult. Therefore, the US expanded its base network by linking the right to use bases with peacetime alliances. Denmark, Portugal, Iceland, etc., were, to some extent, positioned as NATO members because of the strategic importance of their bases. In this sense, it is a state of “no alliances without bases,” and the post-war alliance network can be considered inseparable from the maintenance and expansion of the base system.

Further, for the military, alliances were the means, not the end. The military valued not the alliance itself but the right to freely use the base, and, in that sense, the idea of “reluctantly joining the alliance to gain the base” existed as well. From this perspective, post-war peacetime alliances can also be considered an institutional framework to maintain the base network.

6. The Future of Alliances and Bases in the Trump Era

Based on the above, peacetime alliances and base deployments in Europe can be understood as an exceptional phenomenon formed during an era when spheres of influence did not exist. Conversely, the deployment of bases in the Western Pacific is based on the logic of the US defending its own sphere of influence, and it differs from the situation in Europe.

However, if, in the future, some kind of separation of spheres of influence were to be established, there is no guarantee that conventional forward deployment will be maintained in the Western Pacific. Nevertheless, even in that case the base rights themselves will likely be maintained while the importance of access and joint use will likely increase. Furthermore, while considering the possibility that US regional engagement will decrease relatively, it will remain essential to strengthen cooperation between Japan, South Korea, the Philippines, Australia, etc., and design a system to “keep the seat warm.”

(This is an English translation of an outline of the lecture delivered by Dr. KAWANA Shinji, Professor, Department of Political Science, Faculty of Law, Daito Bunka University, at the 111th Policy Plenary Meeting of CEAC on May 28, 2026.)