The Security Treaty between Japan and the United States was signed in September 1951, written to come into effect simultaneously with the San Francisco Peace Treaty that ended the Allied Occupation of Japan after World War II. The bilateral security relationship forged at that time has been called one of the most stable alliances in the world.

Far from losing its raison d'être after the collapse of the Soviet Union and the end of the Cold War, it has taken on increased significance, evolving from a bilateral relationship to one of the pillars of peace and stability in the Asia-Pacific region. Yet the alliance is built on an arrangement that was problematical from the beginning and that remains a serious source of tension and instability: the high concentration of US bases in Okinawa.

In late April 2012, the foreign and defense ministers of Japan and the United States signed a joint statement setting forth Washington's commitment to redeploy approximately 9,000 US marines from Okinawa Prefecture to locations outside of Japan and to return all or part of six US military installations in the same prefecture.

One might imagine that the people of Okinawa, who have long chafed under their disproportionate burden, would rejoice at the prospect of a reduction in troop strength and the full or partial return of several bases. In fact, the reaction has been one of disappointment. To understand why requires a bit of historical background.

Six Decades of Friction

Between March and June 1945, as World War II was entering its final stages in the Pacific theater, the people of Okinawa were caught up in fierce fighting between Japanese and US forces. The final death toll of that battle was on the order of 200,000, including tens of thousands of local civilians. But even after the war was over, Okinawa's hardships continued. Okinawa as a whole remained under the control of the US military until 1972, and much of it remained that way even after the prefecture was finally returned to Japanese sovereignty.

In fact, more than 70% of all US military installations in Japan are concentrated in Okinawa Prefecture. Moreover, because many of those bases are adjacent to urban and residential areas, the residents have complained for years about ground and air pollution, safety concerns, noise from aircraft, and crimes committed by base personnel.

At the same time, the military bases on Okinawa have played a crucial role in the US security strategy, owing to their proximity to China, the Korean Peninsula, and Southeast Asia. For the US military, free access to those bases has been critical in maintaining a presence capable of responding to and thus deterring threats in the region. For this reason the US military cannot simply pack up and go home.

For years the conflict simmered. The residents of Okinawa regarded the US bases and their personnel as ongoing obstacles to peace and tranquility. The prefectural and municipal assemblies consistently called for the US bases to be scaled back. That these pleas fell on deaf ears during the Cold War perhaps goes without saying, but the end of the Cold War brought no relief for the prefecture. As a result, anti-American sentiment has continued to mount among the residents.

A turning point came in April 1996, when Japan and the United States signed an agreement concerning the closure of US Marine Corps Air Station Futenma, located right in the middle of the city of Ginowan in Okinawa. Under the agreement, the United States was to return MCAS Futenma, provided Japan supplied another base to replace it. The deal was reached in response to intense local anti-American feeling provoked by the rape of a local schoolgirl by three American servicemen the year before.

After the agreement was signed, the Japanese government began to explore concrete options for the relocation of MCAS Futenma (including a new heliport slated for construction there). The most promising candidate seemed to be a site offshore from the Henoko district, a quiet coastal area in northeastern Okinawa. The government spent much time and effort attempting to line up local support for the plan, but each time it seemed to be making progress, opposition to the idea of another base in Okinawa would flare up, resulting in another setback.

Compromise Achieved and Lost

Then, in 2006, a full 10 years after the initial relocation agreement, the Japanese and US governments formally agreed on a plan under which MCAS Futenma would be closed and a replacement facility built in Henoko. Of the marines stationed at Futenma, 8,000 were to be transferred to Guam, and the Japanese and US governments were to share the cost of building new facilities on Guam to accommodate the additional personnel.

After years of negotiation, the government had managed to overcome fierce resistance and secure the necessary local support for a move to Henoko. Although the solution would not reduce the number of bases in Okinawa, it did promise a scaling back of the US military presence and relief for the residents of Ginowan.

Then came the 2009 general election that swept the Liberal Democratic Party from power and put the Democratic Party of Japan in control of government. DPJ leader Yukio Hatoyama took over as prime minister in October 2009, and suddenly everything was back at square one.

During the general election campaign, Hatoyama had blithely rejected the 2006 bilateral agreement with a public statement calling for the relocation of MCAS Futenma "outside of Okinawa Prefecture at the very least." Once in power, Hatoyama tried negotiating various alternatives to Henoko, such as an island off Kagoshima Prefecture, but failed to win approval at the local level.

As the relocation process ground to a halt, Washington's impatience was unmistakable. Finally, in May 2010, both governments agreed again that the new base would be built off Henoko. By this time, however, the residents of Okinawa had been led to expect nothing less than the base's removal, and Hatoyama's flip-flop triggered a major backlash.

The new government's thoughtless policy shifts had made the previously agreed relocation plan unfeasible. The debacle contributed to Hatoyama's fall, and neither of his successors—first Naoto Kan and then Yoshihiko Noda—have been able to break the stalemate. The situation surrounding MCAS Futenma remained unchanged since 1996, and Washington's impatience and annoyance continued to mount.

The Japan-US Alliance in the Post–Cold War Era

The end of the Cold War freed the countries of Western Europe from the threat of Soviet aggression and opened the way for a major shift in that region's security policies. But it brought no respite for Northeast Asia. Indeed, between China's military expansion and modernization and North Korea's nuclear weapons and missile programs, security concerns in the region have only intensified.

Today the Japanese and US governments are particularly concerned about moves by China to assert control over the East China and South China seas, create conditions preventing strategic access by other countries, and develop anti-access and area denial (A2AD) capability that could deny Japanese, US, and other ships access to bordering seas as well. But neither the United States nor Japan is in a position to spend aggressively on military or defense capability in order to counter these moves. In Washington, legislation passed by Congress last year could result in draconian cuts in the US defense budget. In Tokyo, there is strong and mounting pressure for fiscal rehabilitation to rein in Japan's burgeoning public debt.

In recent years the US military, exploiting new technological developments, has shifted from widespread permanent overseas installations equipped for large-scale conflicts to a more mobile, flexible force consisting of numerous rapid-response units capable of reacting quickly to any situation. At the same time, the modernization of China's military has placed MCAS Futenma and its 18,000 marines within range of Chinese ballistic missiles, and some US military experts have warned that it could be a prime target in the event of an attack on Taiwan or some other regional conflict.

In other words, in the context of China's modernized military, the heavily populated Japanese bases that once functioned as a deterrent are turning into a potential liability for the US military. Relocation of US Marine Corps units outside the range of Chinese ballistic missiles has thus become an important agenda item in the ongoing realignment of US forces. But under the 2006 agreement, the transfer of Marine Corps personnel was predicated on the relocation of MCAS Futenma. Japan's failure to honor its original relocation commitment owing to domestic circumstances was preventing the United States from proceeding with the transfer of marines to Guam and other bases.

This, then, was the basic impetus behind the Japan-US agreement signed last April. The purpose was to uncouple the transfer of Marine Corps personnel from the base relocation plan so as to ensure that the realignment of US forces—specifically, a reduction in the number of marines stationed in Okinawa—could proceed regardless of when or how the MCAS Futenma relocation issue was resolved.

In concluding the April agreement, Washington was essentially saying, "The Japanese government has made no progress overcoming domestic obstacles to the relocation of MCAS Futenma. The current situation exposes the marines on Okinawa to unacceptable risk. That being the case, we are uncoupling the two issues and proceeding with the transfer of marines. Solving the Futenma base problem is not Washington's problem."

For the people of Okinawa, the April agreement was a disappointment because it made it clear that the relocation of MCAS Futenma had been placed on the back burner. If a helicopter were to crash near the air base (such things have happened in the past) in the middle of densely populated Ginowan, hostility toward the US forces in Japan, and toward the Japan-US alliance itself, would rise to new heights, not merely in Okinawa but throughout the nation.

Yet this alliance is more important to East Asia than ever before, given China's growing power in the region. Indeed, Defense Minister Satoshi Morimoto, appointed during Noda's recent cabinet reshuffle, has stated repeatedly that the US military's continued access to its bases in Japan is of great importance to the security of Northeast Asia.

Today as in the past, the Okinawa problem threatens to undercut the very foundations of the Japan-US security relationship. Yet rather than work to resolve the issue, both governments have left it to fester. It is not a situation to inspire confidence in the strength of the bilateral alliance.