Hundreds of rocky islands, islets, sandbanks, reefs and cays lie scattered across Asia's eastern waters, unimportant looking to the naked eye but significant enough to spark what may be the most worrying deterioration in US-China relations in decades.
China's military rise and its increasingly assertive claims to sovereignty of these largely uninhabited lumps of rock, coral and sand have set it on a possible collision course with its neighbours, who also make various claims to parts of the archipelagos, and with the United States, which has important alliances with three of the rival claimants and would be obliged to defend them in case of an attack.
As Chinese and Vietnamese ships ram each other in the contested waters, and Chinese and Japanese fighter jets play games of chicken in Asia's disputed skies, the risk of military escalation is growing. Even more significantly, the stand-off is generating bad blood between Washington and Beijing and could torpedo cooperation on important global issues, including the Middle East, climate change and nuclear proliferation.
With US Secretary of State John Kerry and US Treasury Secretary Jack Lew visiting Bejing for the sixth annual Strategic and Economic Dialogue meeting, some say the US-China relationship is facing its stiffest test since President Richard Nixon travelled to Mao Zedong's China in 1972.
"US-China relations are worse than they have been since the normalisation of relations, and East Asia today is less stable than at any time since the end of the cold war," said Robert Ross, a political science professor at Boston College and associate of Harvard's John King Fairbank Centre for Chinese Studies. The Obama administration's foreign policy rebalance, or "pivot," to Asia has been widely interpreted in China as an attempt to contain its rise.
US efforts to bolster ties with regional states such as Vietnam and to reassure nervous Asian allies such as Japan and the Philippines that it stands ready to defend them militarily have created a new narrative in Beijing - that the United States has encouraged China's neighbours to push their territorial claims more aggressively.
"It is clear that the disputes are between two sides, but the United States is taking sides, and it is not impartial," Admiral Sun Jianguo, the deputy chief of the general staff of the People's Liberation Army, said.
In Washington, a rival narrative is taking hold: that China is intent on pushing its territorial claims through the threat of military force and that it ultimately wants to push the US out of Asia.
There have been more intense past crises in US-China relations, including the fallout from the 1989 Tiananmen Square crackdown, but none, perhaps, as fundamental as this.
Last November, China spooked its neighbours by announcing an air defence identification zone over the East China Sea, including over islands administered by Japan.
In March, the Chinese coastguard tried to block Philippine vessels from resupplying soldiers stationed on the disputed Second Thomas Shoal. Two months later, it deployed a US$1 billion deep sea oil drilling rig into disputed waters off the Vietnamese coast and Beijing has also been building artificial islands in the South China Sea that US officials say are meant to strengthen its sovereignty claims.
China argues it has historical claims to a huge swath of the South China Sea, but its recent assertiveness has puzzled experts, appearing to undermine last year's efforts to promote a more cooperative, development-focused relationship with its neighbours.
Some argue that President Xi Jinping may see external threats as useful in ushering in tough reforms, including of the military, while others say that China is simply baring its fangs as it seeks to build a new Asian order in which it, not the United States, is the major player in the region.
Most agree, though, that China is asserting itself partly because it now possesses a modern deep water navy and professional coastguard.
But China's rise has left the US caught between its commitments to allies and its desire to maintain a constructive relationship with China. In recent months, it has seemed to emphasise the former, sending B-52 bombers to fly through China's air defence zone and threatening to reevaluate its military posture in Asia if China extends the zone to the South China Sea.
In April, President Barack Obama visited US allies Japan, South Korea and the Philippines in a trip that pointedly excluded China. While in Japan, he became the first president to explicitly say that the US defence treaty covered the uninhabited Diaoyu Islands in the East China Sea, which are claimed by both China and Japan, which calls them the Senkakus. In the Philippines, he signed a new 10-year defence agreement.
Beijing has since hit back. When US Defence Secretary Chuck Hagel implicitly accused China in May of "intimidation, coercion or the threat of force" in asserting its territorial claims and warned that the United States "will not look the other way when fundamental principles of the international order are being challenged", Lieutenant General Wang Guanzhong called Hagel's comments "excessive" and "suffused with hegemony, incitement, threats and intimidation", China Central Television reported.
Daniel Russel , assistant secretary of state for East Asian and Pacific affairs, argues that the blunt exchanges between the two countries could be beneficial.
"It is an indication of health, I believe, that we are able to be so direct with China, without fearing that we are tanking the relationship or the prospects for cooperation," he said. "We do not pull our punches, but at the same time we are working hand-in-hand with China wherever we can."
The US should have been more assertive in forging closer economic links with Asia through a Trans-Pacific Partnership (TPP) trade deal and with China through a bilateral investment treaty, some critics say.
"We need a lot more weight on the economic side, because that's what keeps your relationship from tipping into a cold war relationship," said Christopher Johnson, of the Centre for Strategic and International Studies.
Fuelling China's adventurism is also a feeling among some Chinese officials that the US lacks resolve. They point to the administration's unwillingness to punish Syria for using chemical weapons and its failure to prevent the Russian invasion of Crimea as showing it to be a "paper tiger", said Johnson, the CIA's former top China analyst.
"They believe Obama is fundamentally weak and [un]interested," he said. But, Johnson added, Beijing would be wrong to underestimate the US commitment to defend Asia. "America is a sleeping giant," he said, "and if you prod us too hard, we are going to mobilise."
Either way, foreign policy experts agree that the relationship deserves more attention than it is getting. Kerry is seen as more interested in the Middle East, while national security adviser Susan Rice has yet to visit Beijing.
Meanwhile, Obama's refusal to come to China for a return version of last year's Sunnylands summit with Xi has also "personally irritated" his Chinese counterpart, said Johnson - although the president is scheduled to visit Beijing for an Asia Pacific summit in November.
With that visit, at least, and with this week's Strategic and Economic Dialogue, the administration has a chance to focus minds on one of its most serious foreign policy challenges, experts say. "Summits," said Ross "have the value of making presidents pay attention."