By Brad Glosserman, Special to CNN

Editor's note: Brad Glosserman is executive director of Pacific Forum CSIS, a Honolulu-based think tank that focuses on U.S. foreign policy and Asia. The views expressed are his own.

For much of the postwar era, numerous U.S. security officials and analysts argued that Japan was a “free rider” in its alliance with the United States. Yet although the alliance is unequal, this charge goes too far. After all, the treaty establishing the security relationship between the two nations acknowledged the limitations imposed by Japan’s “Peace Constitution,” which officially forswears war as an instrument of state policy. (And don’t forget this Constitution was forced on Japan by the United States during the occupation).

In practical terms, the United States is obliged to come to Japan’s defense in the event of an attack on its territory, while Japan is under no similar obligation if the U.S. is attacked. In return, however, the United States has forward bases on Japan, which makes the island, in the words of one former prime minister, “an unsinkable aircraft carrier.”

U.S. complaints about burden-sharing reached a crescendo during the 1980s and ’90s as Japan’s economy looked like it might eclipse that of the U.S. Those fears ebbed over the last two decades as Japan entered the doldrums and American attention switched its focus to China.

Little noticed in the United States outside a community of security specialists has been the evolution of Japan’s security posture. Since 1996, the U.S. and Japanese governments have been working to reapportion roles and missions in ways that allow Japan to do more in its own defense and contribute more to regional security.

This effort takes a number of forms – and there’s still more to do – but it begins with an increasingly realistic mindset among Japanese security policymakers. A nation once derided as pacifist has come to realize that it can’t rely on goodwill to secure good relations among nations, and it’s increasingly cognizant of threats to national peace, security and prosperity posed by states in the region and bad actors. North Korea’s belligerence and bellicosity have been instrumental in shaping Japanese thinking, as has China’s determination to assert its national interests, even if it risks confrontation with Japan. China’s military modernization effort, which seems disproportionate to regional threats and whose endpoint and purpose aren’t clear, compounds the unease.

Japan’s new thinking is evident in the Defense White Paper that was published late last month. It is, from a U.S. perspective, an unremarkable document, one that puts the alliance with the U.S. at the center of Japan’s defense policy and explicitly reaffirms at multiple points and in many ways the overwhelmingly defensive orientation of its security outlook. Yet it’s also striking for the blunt way it questions Chinese intentions and the assertion that Japan needs better defense capabilities to prepare for and respond to security challenges and contingencies.

The problem is that language that sounds like boilerplate to many Americans has inflamed China. A spokesperson for the Chinese Foreign Ministry, for example, denounced the White Paper, calling it “groundless” and “irresponsible.”

Where Americans see a gradual movement in Japanese defense policy, Chinese – and Koreans – see the re-emergence of a militarist Japan. So, for example, when Japan amended its Atomic Energy Law in the aftermath of last March’s Fukushima Daiichi nuclear power plant disaster and acknowledged that nuclear energy was part of “national security” – a seemingly obvious conclusion since a stable energy supply is critical to a functioning economy – Chinese and Koreans asserted that Japan was laying the foundation for the acquisition of nuclear weapons. Given the “allergy” that dominates Japanese thinking about all things nuclear and the deep scars of World War II, it’s hard to imagine a more fanciful proposition.

In recent discussions in Beijing, though, Chinese interlocutors warned that the U.S. risked being dragged into a confrontation with China as a result of Japan’s determination to assert its claim to the Senkaku islands, territory known as the Diaoyutai to Chinese, and also claimed by Beijing. Tokyo’s behavior was equated with that of Pyongyang, and it was apparently up to both Washington and Beijing to rein in their respective allies.

Equating the actions of those two nations seems unreal. But it’s a good example of the kind of thinking going on in Northeast Asia right now.