In Japan-U.S. relations, there is an often-heard argument that the United States is controlling Japan to prevent it from becoming a military superpower. In fact, Washington has played a contradictory role, demanding that Japan increase its defense spending and other contributions to the alliance, while at the same time opposing Japan’s deployment of aircraft carriers and long-range missiles. However, since the 1990s, as the international environment has changed, Japan and the U.S. have become increasingly integrated, and Japan has sought to strengthen its military capabilities.
With the return of the Trump administration, this trend has become even stronger. What does Japan’s defense buildup mean for its relationship with the United States – and Japan’s potential to become an independent military power?
The “Cap in the Bottle” Theory?
The “cap in the bottle” theory holds that the Japan-U.S. Security Treaty and the commitment of U.S. forces in Japan have prevented Japan’s military buildup and ensured stability in the East Asian region. This idea has existed since the early days of the alliance.
The theory got its name – and its most famous articulation – in an interview given to the Washington Post in March 1990 by Major General Henry Stackpole III, a U.S. Marine Corps officer in Japan. Stackpole warned that, if the U.S. military were to withdraw from Japan, Tokyo would further build up “what is already a very, very potent military.” He added: “No one wants a rearmed, resurgent Japan… So we are a cap in the bottle, if you will.”
Stackpole continued, “None of Japan’s neighbors wants a rearmed Japan, so if we were to pull out of the U.S.-Japan Security Treaty, it would definitely be a destabilizing factor in Asia.”
It’s important to note the historical backdrop for this interview. With the Cold War coming to an end, there were calls for peace dividends, such as the reduction of U.S. forces stationed overseas. Thus Washington was seeking to find a rationale for the Japan-U.S. alliance that didn’t hinge on containment against the Soviet Union.
At the same time, the United States was concerned about Japan’s military rise. The end of the Cold War brought concern that Japan, which had emerged as an economic superpower, would rise militarily as the threat from the Soviet Union, its main security threat at the time, diminished. Looking at the subsequent slump in the Japanese economy and the continued strengthening of the Japan-U.S. security relationship, the prediction did not come true. In the uncertain transition period of the early 1990s, however, some pundits were predicting that Japan would become a military power and become independent from the United States.
The “cap in the bottle” theory was proposed in this context, but similar ideas had long been expressed by U.S. policymakers. One famous example is the China-U.S. rapprochement promoted under the Nixon administration. President Richard Nixon himself recommended that, during initial contacts, the U.S. should build on China’s “fear of a resurgent and militaristic Japan.” He wanted to stress to Chinese officials that:
In the case of Japan it is obvious that they have both the ability, resources, and know-how to rebuild their military in a precipitous fashion and that a total disengagement of the United States or a misapplication of forces in the area could result in a resurgent Japanese bellicosity with considerable danger for all.
In other words, U.S. officials argued in their talks with China that the U.S.-Japan security treaty existed to prevent Japan from becoming a military power in Asia.
The “cap in the bottle” theory is not just a rhetorical concept; it has real implications for Japan’s developments in the security sphere. As postwar Japan developed its military power, the intentions of the United States were important. For Japan, the U.S. was not only an ally but also a supplier of cutting-edge weaponry. For example, when the Japanese Maritime Self-Defense Force built naval vessels, it exchanged opinions with the U.S. Navy, and the U.S. side sometimes gave orders. The U.S. supplied Japan with cutting-edge technology such as the Aegis system; to keep the supply flowing, Japan had no choice but to comply with the U.S. wishes.
Since the 1970s, the United States has avoided making extensive commitments overseas and has instead encouraged its allies – including Japan – to become more independent. However, from Washington’s point of view its allies were to serve as a complement to the U.S., not move toward complete security independence. Thus Washington has walked a fine line: encouraging its ally Japan to strengthen its defense capabilities while keeping Japan under control.
Has the Bottle Cap Been Lifted?
For decades, the U.S. has demanded that Japan strengthen its defense capabilities, including an increase in defense spending. However, the security environment in East Asia has changed markedly since the 1990s, thanks to North Korea’s nuclear and missile programs and China’s military rise. Under these circumstances, Japan shifted from responding to threats to the north, with the Soviet Union as the main enemy, to focusing on threats to the south.
In responding to China, it was essential for Japan to defend its outlying islands, scattered from Kyushu to Okinawa and close to Taiwan. However, the distance from the southernmost point of Kyushu to Yonaguni Island near Taiwan is over 1,000 km, and existing weapons systems alone were not sufficient. Therefore, Japan decided to acquire an aircraft carrier capable of deploying vertical takeoff and landing aircraft as well as long-range missiles. Japan had never possessed either of these weapons, even though there have been requests for them. Moreover, none of these items could be acquired without the consent of the United States.
That said, these capabilities are not necessarily under U.S. control. Take, for example, Japan’s long-range missiles. While deploying the Joint Strike Missile (JSM) mounted on the F-35 and the U.S.-made Tomahawk, Japan has also been deploying an improved version of the domestically produced Type 12 surface-to-ship guided missile. In addition, Japan has stated that it will operate its own long-range missiles.
Since the 2000s, Japan has rapidly developed its defense capabilities, but at the same time, questions have been raised about U.S. involvement. The first Donald Trump administration stated that it would ask U.S. allies to bear more of the burden for their own defense. Japan responded by announcing an increase in defense spending, citing change in the international situation with the rise of China and Russia’s invasion of Ukraine. The subsequent Biden administration stressed the importance of U.S. allies, but its basic policy line was the same as that of the Trump administration: allies should do more. With the second Trump administration now in power, it has called for Japan to provide even more for its own defense.
What Will Happen After the Cap Is Lifted?
Summarizing the developments to date, it can be said that Japan is strengthening its military power in response to the United States’ demands, and as a result Japan’s defense capability is moving toward self-reliance – the exact worry of pundits expressing the “cap in the bottle” theory.
Of course, the Japanese government and experts in the Japanese security community still state that Japan is solely focused on the Japan-U.S. alliance. Tokyo has never changed its stance of focusing solely on the Japan-U.S. alliance, rather than seeking to become an independent actor in the security realm. However, the second Trump administration is moving in the opposite direction of a loyal ally.
Yet it’s important to note that this is not the first time the U.S. has taken this stance. While forcing Japan to strengthen its defense capabilities and bear the cost of U.S. forces stationed in Japan, Washington has on numerous occasions neglected Japan – for example, by negotiating with China over Japan’s head. Japan nevertheless continued to support the United States as a loyal ally, despite these historical frictions.
The second Trump administration’s policy toward Japan has only just begun. As usual, the president and his policy makers are continuing to ask Japan to shoulder the burden, while remaining vague about their own responsibilities. Meanwhile, Japan continues on its path of self-reliance. As these trends continue, we may see in detail what happens when the “cap in the bottle” comes out.