While foreign-policy experts and risk analysts were riveted by the nuclear talks with Iran last weekend, the next major geopolitical crisis erupted a world away, over a clump of desolate islands in the choppy waters between Japan and China.
With the United States dispatching two B-52s to reinforce its protest over China's attempt to control the airspace over the islands, it served as a timely reminder that President Obama wants to turn America's gaze eastward, away from the preoccupations of the Middle East.
Mr. Obama's shift — once known as a pivot, now rebranded as a rebalance — has always seemed more rhetorical than real. But when Vice President Joseph R. Biden Jr. travels to China, Japan and South Korea next week, the administration will have another chance to flesh out the policy.
"What isn't clear to me is whether they see this as a Japan-China problem that needs to be managed or as part of a longer-term test of wills with Beijing," said Michael J. Green, an Asia adviser in the administration of President George W. Bush who is now at the Center for Strategic and International Studies.
If it is the latter, Mr. Green said, the United States needs to project military power in the region, build up the defensive capacities of allies like Japan and the Philippines, and align the countries that ring China's coastal waters to present a united front against Beijing's aggression.
The trouble, he added, is that "the administration is very worried about appearing to contain China."
The cause of all this trouble are the flyspeck Senkaku Islands, which Japan administers but that China, enticed that they may sit atop rich mineral reserves, now claims, calling them the Diaoyu Islands.
The dispute has mushroomed into a dangerous standoff between the world's second- and third-largest economies — one that rekindles old resentments over the World War II conduct of imperial Japan and pits a conservative Japanese leader, Shinzo Abe, against a Chinese president, Xi Jinping, who is riding a nationalist tide in his country.
With so much at stake, Mr. Biden's advisers say the dispute will intrude on every meeting he has in the region. That could come at a cost to an agenda that includes promoting a trans-Pacific trade deal and discussing how to deal with the nuclear threat in North Korea. Mr. Biden must also decide how to handle the bitter animosity between Mr. Abe and South Korea's president, Park Geun-hye.
"There's an emerging pattern of behavior that is unsettling to China's neighbors," a senior administration official said on Wednesday, previewing Mr. Biden's message. At the same, he added, "The vice president of the United States is not traveling to Beijing to deliver a démarche," a diplomatic term of art for a slap on the wrist.
The delicate balancing act in Mr. Obama's Asia policy, between cooperating with and containing China, is evident in the administration's mixed messages over the last two weeks. Speaking before Beijing's latest provocation, the national security adviser, Susan E. Rice, said the United States was seeking "a new model of major power relations."
"That means," she said in her maiden speech on Asia, "managing inevitable competition while forging deeper cooperation on issues where our interests converge."
Referring to the territorial disputes between China and its neighbors — which flare up not only with Japan in the East China Sea but also in the South China Sea, with the Philippines and Vietnam — Ms. Rice urged "all parties to reject coercion and aggression and to pursue their claims in accordance with international law and norms."
To some critics, that smacked of moral equivalence: the coercion and aggression have been overwhelmingly on the part of China against its smaller neighbors. But on Saturday, when Beijing announced an "air defense identification zone" over a wide section of airspace above the islands, the United States jumped off the fence.
Secretary of State John Kerry immediately condemned what he called an "escalatory action" by China and Defense Secretary Chuck Hagel said the United States would not alter any military operations because of it, a promise he kept this week by dispatching the unarmed bombers from Guam on a routine mission off the coast of China.
Administration officials said it was important to push back against China's dubious assertion of jurisdiction over international airspace. The Chinese policy requires foreign planes flying through the zone to identify themselves and file a flight plan, even if they are not flying into Chinese airspace.
The symbolism of B-52s' flying, with no advance warning, through China's zone spares Mr. Biden from having to play the tough guy. But experts said he needed to leave no doubt in talks with President Xi that the United States thinks the Chinese move was ill advised.
"It will have the Chinese scrambling aircraft time after time, especially if the Japanese play games with it," said Kenneth G. Lieberthal, a China adviser during the Clinton administration.
The vice president has firsthand experience of this. On a visit to Beijing in 2011, he presented Chinese officials with photographs taken by American pilots that documented how Chinese fighters, dispatched to intercept American planes flying surveillance missions off China's coast, sometimes came within 10 feet of their wingtips.
(Read more: US, Japan slam China airspace rules on islands)
Mr. Biden has cultivated an unusually personal relationship with Mr. Xi. The two traveled together in China and the United States, when Mr. Xi was vice president. That may make Mr. Biden more alert to the domestic political pressures the Chinese leader faces, as he embarks on risky economic reforms after a recent Communist Party congress.
"Chinese social media, official and semiofficial media are all playing up this dispute," said Cheng Li, a senior fellow at the Brookings Institution. "The U.S. has failed to understand how much weight the sovereignty issue carries with Asian countries."
The tensions are likely to increase. The Chinese Navy has put its only aircraft carrier out to sea, on a course toward the South China Sea. In the East China Sea, an American carrier group is joining Japanese warships for long-planned naval exercises.
With so much firepower in such hotly contested waters, experts said there was a real danger of miscalculation by either side. Mr. Biden, who will begin his trip in Tokyo, is expected to urge Mr. Abe to show restraint as well.
(Read more: China's reforms: 5 key ones you should know)
The good news for all concerned, China experts said, is that Mr. Xi is much less interested in military adventurism than in overhauling China's economy. "The chances of a real war are still low," Mr. Li said. "But sometimes incidents will push leaders into a corner."