China has been happy to engage with the US on economic issues, joining the World Trade Organisation and stockpiling Treasury bonds, but Beijing has also accelerated a military build-up that has the US in its sights. Rather than preparing for a fight with the US, Chinese planners want gradually to squeeze the US out of its dominant position in Asian waters by developing a series of missile systems they describe as "anti-access" weapons.

Yet in the last year or so, China's charm offensive in Asia has run into trouble - not least in the South China Sea, which for many Asian countries is a barometer of how a powerful China might treat them. The Paracel and Spratly islands are claimed in full or in part by Vietnam, Malaysia, the Philippines, Taiwan and Brunei. On China's maps, however, the islands are inside a U-shaped line of its territorial waters, which stretches down to cover most of the South China Sea.

Amid rising tensions, China has reportedly told other Asian countries not to discuss the issue among themselves. According to US officials, Beijing also now says it considers the area a "core interest", alongside Taiwan and Tibet. Some push-back was inevitable. Sure enough, Vietnam - the one country in the region with a Leninist political system comparable to China's - lobbied its old nemesis in Washington to get involved. (The USS George Washington aircraft carrier visited Vietnam at the weekend.) Even Singapore's Lee Kuan Yew, who has spent much of the past decade praising Beijing, called last year on the US to remain the Pacific's "superior power".

In Asia's new diplomatic contest, the momentum is still very much with Beijing. While the US faces debts and deficits, China could easily grow by 8 per cent a year for one if not two more decades and its naval power will also inexorably expand.
Yet Mrs Clinton has laid a trap for Beijing in the South China Sea. If China stands up to US interference in its backyard and presents itself as the regional power, it risks pushing wary neighbours into the US camp. Indeed, this is the broader diplomatic test that China faces in Asia over the coming decades. The more dependent Asian countries become on China's economy, the more uneasy they will be about its power. The ball is very much now in Beijing's court.

David Fuller's view As with some other conflicts, this is primarily about oil. It has been simmering for many years, like a live but mostly quiet volcano, which needs to be monitored closely.