TOKYO - US President Barack Obama's Asian tour which starts in Japan on Wednesday has lifted the lid on a bubbling cauldron of regional animosities, exposing historical rifts that Washington can no longer paper over.
Obama touches down in Tokyo a day after nearly 150 lawmakers paid homage at a shrine regarded by neighbouring nations as a symbol of Japan's brutal imperialist past, and shortly after the prime minister made an offering to the controversial site.
In another sour note, China on the weekend seized a huge Japanese freighter over what a Shanghai court says are unpaid bills relating to Japan's 1930's occupation of vast swathes of the country.
Lurking in the seas to the far southwest are coastguard boats - with armed naval vessels at the ready - playing out a volatile dispute between Tokyo and Beijing over ownership of a small chain of East China Sea islands.
And to the west, an ever-unpredictable North Korea which has denounced the presidential tour as "reactionary and dangerous" appears to be trying to seize the spotlight with preparations for a fourth nuclear test.
But despite the increasingly tense security situation and the need for unity, getting top regional allies South Korea - Obama's next destination - and Japan to talk to each other is tricky.
South Korean President Park Geun-Hye and Japanese Prime Minister Shinzo Abe have met just once since both came to power over a year ago, and only then when the US leader cajoled them into a choreographed photo op.
East Asia is a tumultuous region with a multitude of fractures that the US has done little to mend over the last half century, said Christian Wirth, a research fellow at Griffith University in Australia.
"Since the establishment of the postwar regime in San Francisco in 1951 and the onset of the Korean War in 1950, (the US has been) directly and deeply involved in East Asian politics," he told AFP.
"Washington's preference for bilateralism has contributed to the lack of intra-Asian cooperation and historical reconciliation."
'Fears of containment'
In recent decades, foreign policy focus shifted to perennial hotspots like the Arab world, and despite the Obama administration's vaunted "pivot" towards the region, East Asia is feeling a little neglected.
The Middle East still draws a large measure of US attention, and the Ukraine crisis has rekindled interest in Europe. The cancellation of Obama's visit to the region last year to deal with a domestic budget battle didn't help.
But worse, "the so-called 'pivot' or 'rebalancing', is causing more confusion and increases tensions rather than stabilising an already dynamic region", said Wirth.
"It heightens fears of containment on the part of China and increases expectations of military protection, and at times lends itself to assertive policies on the part of some US allies."
On this trip, Obama has to walk a tightrope between calming Chinese fears of US encirclement and bolstering Japan.
Manila, the final leg of the tour, will also be looking for reassurances from its protector in chief. Having mounted a plucky stand over disputed South China Sea reefs against the might of Beijing, the Philippines needs to be told the US still has its back.
Tokyo also worries that Washington may not offer wholehearted support if push came to shove over the Japanese-controlled Senkaku islands, which Beijing claims as the Diaoyus.
Historical interpretations keep muddying the Japan-China relationship, said Washington-based international affairs analyst Taylor Washburn.
"The United States faces a dilemma, in that it wants to make clear its unwavering commitment to Japan's security in the face of destabilising behaviour by China, yet it is also frustrated by Prime Minister Abe's personal quest to efface dark episodes from his nation's history," he told AFP.
The impounded Japanese ship row reflects anger about past injustices, while for Beijing, the squabble over the Senkakus is directly linked to Tokyo's imperialist march through Asia, with the islands' late 19th century "annexation" marking the start of Tokyo's expansionism.
If Abe can be convinced to rein in unpalatable views on Japan's dark past - such as questioning Japan's use of wartime sex slaves in military brothels - it could help to take some of the heat out of the islands spat.
"Obama will impress upon Abe the strategic value of curbing his cabinet's tendency to push a revisionist historical narrative that downplays the regional suffering caused by Japan's past imperialism," James Schoff of the Carnegie Endowment for International Peace wrote earlier this month.
That same effort would also pay dividends in brokering a detente between Tokyo and Seoul, which would allow a united front against North Korean agitation, said Washburn.
It doesn't have to be a perfect peace, he added.
"The United States should not expect any South Korean leader to be silent in the face of historical whitewashing," Washburn said.
"But if Seoul and Tokyo hold off on all security cooperation until they've come to terms over the past, Northeast Asia will be a more dangerous neighbourhood for both countries in the meantime."