Beyond economic strength and military prowess, one of the precious ingredients in great power relations is credibility. Allies and adversaries should know that you mean what you say. Nowhere is this truer than in east Asia. Barack Obama may bear the thought in mind when he carries the American flag around the region later this month. On the face of it, the US president’s approach is clear enough. Washington’s response to China’s rise has been to engage and hedge — to seek to draw Beijing into the international system while refurbishing its own regional alliances. More recently, Chinese assertiveness in the East and South China Seas has led US policy to tilt towards a sturdier “engage and compete”. Obama’s visits to Japan, South Korea, Malaysia and the Philippines are all about underscoring America’s place as a resident Pacific power.

The trickiest stopover will be Tokyo. Japan is America’s most vital regional ally. Under the premiership of Shinzo Abe it is also becoming its most difficult. If the US wants to constrain China, it is also anxious to restrain Abe. The result is an American posture that seeks to blend credibility with ambiguity. The two do not readily mix. Russia’s annexation of Ukraine has pushed Sino-Japanese tensions off the front pages. The dispute over the Senkaku (Diaoyu in Chinese) islands in the East China Sea and the accompanying arguments over history are no less dangerous for that. Relations have broken down. Chinese officials say they will not be repaired while Abe remains in office. The mutual hostility reaches deep into public opinion. The Japanese prime minister, I heard a senior Chinese official remark at a gathering in Shanghai of the Stockholm China Forum, was guilty of provocation, historical revisionism and militarism. Japan was a threat not just to the region, but to the wider international order.

From Tokyo, the riposte is that Xi Jinping, China’s President, has set a course of unbridled expansionism. China wants to grab territory not just from Japan but also from Vietnam and the Philippines. The intrusive reach of China’s latest air defence identification zone is cited as proof of Beijing’s intent.

Such rhetoric is often stylised. What makes the stand-off combustible — and leaves the US deeply anxious — is the disinterring of the deep resentments of history. China is determined to expunge past humiliations. Abe is unwilling to apologise. The Senkaku dispute is as visceral as it is territorial.

In the short space of a year the Chinese president has amassed more personal authority than any since Deng Xiaoping. Proud of his status as a “princeling”, he has bypassed the machinery of collective leadership and shown scant regard for the views of Communist party elders. Restoring China to the front rank of nations seems to many a natural extension of Xi’s oft-proclaimed “China dream”.

Abe has his own dream. For more than half a century, Japan behaved as the model international citizen, embracing cooperation and eschewing conflict. Abe hails from a different tradition. His brand of nationalism says China’s rise must be matched by Japan’s resurrection. Abenomics at home is to be accompanied by a shedding of the culpability and constraints Japan accepted after the Second World War.

The prime minister’s unapologetic visit to Tokyo’s Yasukuni shrine, which counts war criminals among fallen warriors, and his equivocation about the treatment of Korean “comfort women” have reignited the embers of history. The reaction in Beijing has been matched by anger in Seoul. One of Obama’s tasks this month will be to try to secure a rapprochement between Japan and South Korea. Their shared interests should make them natural allies.

One strain of US thought says that for all its doubts, Washington has no option but to stand by Abe come what may. The US has not taken a view on sovereignty of the Senkaku but is clear that Tokyo’s control of the islands is covered by America’s security treaty with Japan. Standing aside in the event of a Chinese incursion, the argument runs, would carry incalculable costs. China’s ultimate aim is to push the US out of the western Pacific. Giving up the Senkaku would strip the US of regional credibility. Some recall the collapse of British prestige following the fall of Singapore.

So why the present ambiguity about the US response? Simple. If Washington cannot afford to step back, it does not want to offer Abe any incentive to provoke a shooting match. It wants to restrain as well as reassure. Logic says Beijing and Tokyo have their own compelling interest in de-escalation. They are both losers, politically as well as economically, from the rise in tension. China’s assertiveness pushes its neighbours into Washington’s embrace. Abe’s unrepentant nationalism robs Japan of friends. The abiding danger is the familiar one that mistrust begets miscalculation. The military in Beijing and Tokyo already have their war plans in place.

No one can be sure Obama’s precarious balancing act will serve to keep the peace. The risk is that one side or the other will force Washington to choose. Russia’s march into Crimea has raised questions as to where the West would draw the line. Would Nato go to war over the Baltic states?

Much the same is asked in east Asia: Will Obama fight China over a bunch of rocks in the East China Sea? The more credibly the US and its allies can answer “yes” to both questions, the less likely their resolve will be tested.

— Financial Times