Cracks in the Cornerstone.

• Author: Sankey, Evan

Tributes to mark the sixtieth anniversary of the U.S.-Japan Security Treaty last January celebrated the vision of its creators and its modern indispensability. Certainly, the successes are real. The treaty has kept a former enemy and advanced industrial power aligned with the United States and served as the foundation of America's geopolitical position in East Asia. Japan is America's most important ally in the region. But it is also worth remembering that the U.S.-Japan relationship owes a large measure of its success to good fortune. Over sixty years it has never been tested in a great power crisis. And fortune has bred complacency, especially on the American side.

The policy case for the U.S.-Japan alliance is little changed since the end of the Cold War. That view is of a "bases for protection" bargain in which Japanese military restraint and U.S. primacy keep the Asian peace, leavened by occasional American requests that its passive client support U.S. global strategy and improve interoperability with the U.S. military. The growth of Chinese power, the relative decline of America's, and Japan's response have undermined key aspects of this story.

Today, Japanese military power is sufficient to heighten Chinese insecurities but insufficient to help slow or arrest East Asia's deteriorating military balance. The American bases at the core of the alliance bargain are vulnerable to new generations of Chinese precision weapons and a source of crisis instability. And Japan is no longer a reactive state. Alarm at Chinese power, concern about U.S. abandonment, and institutional reforms give the prime minister's office the motivation and capacity to sustain a degree of foreign policy autonomy unthinkable in 1990. The United States risks overindulging Japanese policymakers' appetite for security reassurance vis-a-vis China, to the detriment of regional stability.

The United States has two basic interests in East Asia: keeping the region free from hegemonic domination and preserving peace and stability among the major powers. The alliance with Japan has been our core tool for serving these purposes, but regional security developments should cast doubt on its ability to continue to do so in its current form. Asia's security environment is more fragile than at any time since the Korean War, and America's geopolitical margin for error is shrinking. Our most important alliance needs a critical look before its sixty-year run of good fortune comes to an end.

Acentral rationale for U.S. alliances claims that they inhibit regional security competition by making it unnecessary for allies to build big militaries that could threaten their neighbors. This argument is particularly prominent in discussions of the U.S.-Japan alliance, which has been variously described as the "cork in the bottle" of resurgent Japanese militarism, the "cornerstone" of regional stability, and as an American "sword" paired with a Japanese "shield." Henry Kissinger deployed it on his famous 1971 visit to China, assuring Premier Zhou Enlai that the alliance served Chinese interests by containing Japan. The cork metaphor is now passe, but it remains routine for alliance analysts to celebrate the stabilizing effects of Japan's decision to forgo a military posture proportional to its economic power.

Yet the evidence suggests that Japanese military restraint is overrated. Decades of low Japanese defense spending have not dissuaded China from embarking on a huge military buildup or forestalled a worsening regional security dilemma. The dominant view in Chinese policy circles is that the U.S.-Japan alliance is an increasingly offensive arrangement meant to contain China's rise and restore Japanese military power. This is aggravated by persistent Sino-Japanese tensions over Japan's twentieth-century aggression against China and the gradual expansion of the alliance ambit to cover Taiwan, a core sovereignty and legitimacy issue for Beijing. Western analyses commonly observe that China's military modernization began in earnest after the 1996 Taiwan Strait Crisis. Neglected are further likely motivators: the 1997 expansion of the U.S.-Japan alliance guidelines to include "situations in areas surrounding Japan,"...