A key component of Washington’s military rebalancing strategy, with its shift of emphasis to East Asia, is a robust relationship with major allies. During his recent visit to the region, Secretary of Defense, Ashton Carter, highlighted that aspect. At the top of the list of vital security partnerships is the bilateral alliance with Japan.

However, the U.S. attitude toward Japan playing a more vigorous security role has always reflected a degree of ambivalence. The original draft of the Pentagon’s infamous 1991 planning guidance document stressed the need to prevent any country from even aspiring to challenge America’s dominant position. Although some observers concluded that China was the principal target of such concern, Beijing’s relative weakness at the time and the overall language in the document seemed directed more at what was then the fast-rising, second largest economic power in the world—Japan. Moreover, the Pentagon document was not the only example of U.S. uneasiness about Tokyo playing the role of a great power in the security arena. Just a year earlier, General Henry Stackpole, commander of U.S. Marines in Okinawa, opined that the United States was the “cork in the bottle” preventing a resurgence of Japanese militarism and the fears that such a development would spawn throughout East Asia.

Because of bitter historical memories, China has long been even more wary about a Japanese military revival. Indeed, even during the chilliest days of the Cold War, Beijing provided mixed signals about the U.S. military presence in East Asia. Although Washington’s motive to contain communist (including Chinese communist) influence was evident, and therefore resented, Chinese leaders also seemed to believe that America’s supervision restrained Tokyo and prevented Japan’s rise as a strong, independent military power.

In recent years, U.S. leaders have gradually become increasingly receptive to Japan playing a more active security role. The previous ambivalence faded noticeably during George W. Bush’s administration, and that trend has continued throughout the Obama years. The implicit focus of the rebalancing strategy and other elements of U.S. policy in East Asia is to contain Beijing’s growing power and influence. Washington has looked on benignly as Japanese Prime Minister Shinzo Abe’s government has developed military systems with power projection capabilities, such as the new helicopter carrier; begun to sign arms sale agreements with other countries; and “reinterpreted” article 9 of Japan’s pacifist constitution to permit military missions beyond situations of strict self defense.

The American public, however, remains decidedly ambivalent about Japan playing a more extensive security role. A recent Pew Institute survey found that 47 percent would welcome such a change, in part to alleviate the financial and logistical burdens on the United States, but 43 percent believed that, given Japan’s history of aggression in the twentieth century, Tokyo should strictly limit its military role.

The Abe government’s recent behavior is not likely to reduce the uneasiness in the United States, China, or other countries. Tokyo has adopted an uncompromising stance regarding two contentious territorial issues. One is the dispute between Japan and South Korea over the Dokdo/​Takeshima islands. The other controversy is an even more bitter disagreement with China concerning the Diaoyu/​Senkaku islands. Japan has now escalated ill feelings with the publication of textbooks that assert the alleged Japanese historical and legal claim to those territories in an especially abrasive fashion. Both Seoul and Beijing have expressed sharp complaints about the way those textbooks handle the territorial disputes and other issues. Chinese and South Korean officials warn that the books seem to reflect an attempt to legitimize Japan’s imperial era and its many abuses.

Actions by Abe and some close associates reinforce such suspicions. Measures that have been especially unhelpful include the prime minister’s visits to the Yasukuni Shrine (even though individuals honored there include World War II war criminals); continued reluctance to accept historical responsibility for “comfort women”—young girls from South Korea and other areas, who were forced into sexual slavery to Japanese military personnel during that conflict; and Abe’s indiscreet comments suggesting that Japan was something other than a blatant aggressor in World War II. Some of those incidents have dismayed even usually supportive U.S. officials.

Although there is virtually no danger that Japan will embark on another aggressively expansionist binge, these actions taken together indicate that Tokyo is pursuing an increasingly bold, nationalist agenda. That development is likely to make China, South Korea, and other neighbors nervous. It also may cause mixed emotions in Washington. U.S. leaders no doubt like the concept of a more robust and capable ally in East Asia. However, Japan’s assertiveness can also entangle the United States in problems it would prefer to avoid. For example, Tokyo’s uncompromising attitude on the Diaoyu/​Senkaku issue places Washington in an uncomfortable position. Japanese pressure virtually forced the Obama administration to confirm that the bilateral mutual defense treaty covers those islands—even though their legal status remains very much in dispute. Any armed incident between China and Japan over that issue would create an immediate crisis for the United States.

The regional strategic dynamic has changed in a fundamental fashion. Japan is becoming a far more capable military ally than in previous decades, but U.S. leaders must accept the corresponding reality that Japan also will be a much more independent-minded power with its own policy agenda. Tokyo’s goals may sometimes conflict with U.S. policy preferences or even important U.S. interests. China and other East Asian powers likewise need to realize that Washington’s ability to control Japan’s behavior in the security arena has already diminished and is likely to fade further in the coming years. For good or ill, Japan is emerging as a complete great power, not merely an economic great power. Learning to live with that change will be a challenge for both the United States and the countries of East Asia.