SIXTY years ago this month, a set of agreements signed in San Francisco established the security architecture for Asia and the Pacific that, a few bouts of tinkering aside, is still fundamentally in place. The peace treaty that ended the second world war was accompanied by the formalising of alliances between America and its allies: Australia and New Zealand (the “ANZUS” treaty), Japan and the Philippines. In 1953-54, mutual-defence pacts with South Korea and Taiwan were added, and the ground rules for a Pax Americana in the Pacific were largely complete.

Where to begin enumerating how the world has changed? In September 1951 Chinese and American soldiers were fighting each other in the Korean war, China was “leaning to one side”—that of the Soviet Union—in the cold war, and its economy was largely closed to foreign trade and investment. Now it is the coming power, America's biggest creditor and the largest trading partner for each of Australia, Japan, South Korea and Taiwan.

So you might expect these countries to be reassessing their security ties. Yet rarely, if ever, has any set of countries been so integrated economically with one country, China, while seeking defence guarantees from another, America. All perceive their main long-term threat to be China. This odd dichotomy was the premise of a symposium in Washington this month organised by the Lowy Institute, based in Sydney, Australia, on America's “torn allies”. Lowy's Michael Wesley says the rapid growth of ties with China might “usher in a period of quite agonising choices” for its regional partners. Yet so far there are few signs of conflicting loyalties. Satu Limaye, Washington director for Hawaii's East-West Centre, a think-tank, argues that in fact “the demand for American security has never been higher”.

Indeed, this month Australia and America have been discussing—again in San Francisco—how to enhance their security ties. Japan's new prime minister, Yoshihiko Noda, has indicated that he will make a new attempt to remove the biggest obstacle in Japan's military relations with America, a stalled agreement over relocating American marines in Okinawa. South Korea's president, Lee Myung-bak, is expected to enjoy a state dinner at the White House next month, adding symbolic weight to the importance of the alliance. As for Taiwan, a formal alliance lapsed after America recognised the government in Beijing in 1979. But this week's row over arms sales has shown how even the most China-friendly administration in Taiwan since the civil war still cleaves to the informal American alliance.

Four main things explain America's continuing strategic pull. The first is that, for all the fear of China's rise, the United States remains the predominant military power in the Pacific. If you are buying security, it is the place to shop. Second is the weakness or even hostility of relations among its separate allies. Since a security pact signed in 2007, Australia and Japan have been quietly strengthening military ties. But Japan and South Korea remain testy neighbours. Third, efforts to build up regional security forums, mostly centred on the Association of South-East Asian Nations, have barely managed to start a serious conversation, let alone establish mechanisms for settling disputes.

Fourth, and most important, China has done little to convert its growing economic clout into strategic reassurance. On the contrary, over the past couple of years it has managed to alarm all its neighbours. The potentially placatory government of the Democratic Party of Japan was alienated by China's aggressive behaviour after the detention of a Chinese trawler captain in disputed waters a year ago. South Korea was angered by China's refusal to condemn North Korea for sinking a naval vessel and shelling civilians on one of its islands. Trade and tourism with Taiwan may be booming; but over 1,000 Chinese missiles are still trained on the island. Even countries once far from the American orbit, like Vietnam and India, are being driven closer to it by China's aggressive assertion of territorial claims.

Some of China's apparently inept diplomacy may be a result of poorly co-ordinated foreign policy. But it is also possible to see it as part of a steady and concerted push to assert regional dominance against America. Aaron Friedberg, an American scholar, argues in a new book (“A Contest for Supremacy: China, America and the Struggle for Mastery in Asia”) that China's rulers want to constrict America's military and diplomatic clout in the Western Pacific, “pushing it back and ultimately displacing it as the preponderant power in East Asia”. America, he argues, needs to find “a serious response” to China's military build-up, partly to stiffen the spines of America's friends who may “grow fearful of abandonment, perhaps eventually losing heart and succumbing to the temptations of appeasement.”

Be sure to wear flowers in your hair

Few seem tempted yet. But Gareth Evans, a former Australian foreign minister, has written of a “nightmare scenario” in which policymakers “are forced to choose between their great economic dependence on China and their still-enormous military reliance on the US.” Unlike Mr Friedberg, he argues that “paradoxical as it might seem, the Asia/Pacific region's stability could well be put more at risk by America's continuing assertion of absolute primacy or dominance than by a more balanced distribution of conventional military power.” He quotes, admiringly, Bill Clinton, who once said that America should use its primacy “to create a world in which we will be comfortable living when we are no longer top dog on the global block.”

Top dogs, however, are rarely so prescient; nor are their challengers so accommodating. As a concept, “torn allies” may be somewhat premature. But the tension between celebrating the economic benefits of China's rise and challenging some of its consequences is unlikely to leave the San Francisco arrangements so nearly intact for another 60 years.