The nine-dash line is a vague,U-shaped claim that includes the Spratlys and Paracels,and large sections of Vietnam’s exclusive economic zone,as well as those of Brunei,Indonesia,Malaysia,the Philippines and Taiwan. Originally 11 dashes,it was introduced in 1947 by the Nationalist Kuomintang government and was later adopted by the People's Republic of China. The dashes are symbolic of the fact that the line is a claimed maritime boundary rather than a land border.

When did this lukewarm dispute heat up?

In 2012,China effectively took the Scarborough Shoal from the Philippines after a showdown between Chinese fishermen fishing illegally and the Philippines'Navy. Chinese maritime surveillance vessels entered the waters in support of their fishermen,and then refused to leave even after a deal was brokered by the US – and the Chinese have maintained a presence at the shoal ever since.

The shoal lies a bit over 100 nautical miles from the Philippines,and about 500 nautical miles from China. It hasn't relinquished control since then,with Chinese vessels blocking access to the feature.

Then came China's rapid island buildingand militarisation of its islands,from 2013 onwards. The world watched as satellite photos recorded the development and expansion of these tiny islands,often involving reclaiming land.

The US has maintained an active program of freedom of navigation operations (FONOPs for short) in defiance of China's claim,and in support of south-east Asian claimant states it is allied with – as well as other nearby nations such as Singapore,Australia,Japan,South Korea and Thailand.

In practice,this has meant the US sends its naval vessels to within 12 nautical miles of the islands China has claimed (a nation's territorial sea extends 12 nautical miles from land).

The point of these FONOPs is simple:to send a clear message to China that the US does not recognise its island claims in the South China Sea.

Both China's island building and the US'FONOPs program are described by some analysts as"grey zone"operations and tactics – that is,moves and counter-moves that exist in a state between war and peace and which seek to advance a nation's tactical or political advantage.

As former prime minister Malcolm Turnbullrecently noted,China has created facts on the water in the South China Sea and short of"kinetic action"– that is,war – it's unlikely they'll give up those islands.

So where does that leave other nations?

That doesn't mean that south-east Asian nations should simply give up and cede to China's claims. John Blaxland,a professor of International Security and Intelligence Studies at the ANU,says other countries in the region don't want the US to walk away from its security commitment to the region. That means,in practice,that countries like Australia need to do more.

"We are sending a signal to the US that we want them more engaged,and that we agree with them on the need to push back. If we don’t push back,China will take more,"he says.

"We don't want the US to walk away but the US is getting tired of doing it in the region[pushing back against China] without anyone backing them. This is also a favour for our neighbours,too. They have more skin in the game,less naval capacity,and they are afraid. They are quite happy we are doing it[pushing back against China],but they don’t want to advertise the fact of that."

In late July,during the annual AUSMIN (Australia-US Ministerial Consultations) meeting between Australia and the US defence and foreign ministries,the two countries agreed to conduct more joint military exercises in the South China Sea.

The move followed the decision for Australia to upgrade its long-range missile capabilities at the start of July but,significantly,Australia did not promise to conduct freedom of navigation operations within 12 nautical miles of island features claimed and,in some cases,constructed by China.

How has the argy-bargy played out recently?

Australia submitted a diplomatic note to the United Nations in July that there was"no legal basis"for China to"draw straight baselines connecting the outermost points of maritime features or ‘island groups’ in the South China Sea",which are within its nine-dash-line claim. The submission followed one from the US in June,which argued more forcefully a similar position.

But in fact,there has been a flurry of diplomatic notes submitted,couched in careful diplomatic language,since December 2019 when Malaysia announced plans to establish the limits of its continental shelf,beyond the 200 nautical miles of its exclusive economic zone,in the South China Sea.

Diplomatic notes have also already been submitted by Indonesia,the Philippines and Vietnam,pressing their claims for sections of the sea and rejecting China's;Beijing,in turn,has pushed back and asserted its historic rights to the sea and island features.

Chinese vessels have harassed a Malaysian drilling ship … and sunk a Vietnamese fishing boat. The US,in response,has deployed two aircraft carriers to the region.

While this diplomatic back-and-forth has been going on in the background,China has become increasingly assertive on the water.

Since December,its well-armed coast guard and a fleet of fishing vessels have ventured into Indonesia's North Natuna sea (some of which is within the nine-dash line). This has prompted a furious response from Jakarta,which has done its best to stay one step removed from the South China Sea fight.

Chinese vessels have also harassed a Malaysian drilling ship operating in Malaysia's EEZ,and rammed and sunk a Vietnamese fishing boat. The US,in response,has deployed two aircraft carriers to the region and maintained its program of FONOPs.

All of this has taken place against the backdrop of the global coronavirus pandemic which,some analysts argue,has given China the perfect opportunity to press its claims while other,less rich nations are distracted on the domestic front.

The ANU's Medcalf says that while the issue has been simmering for a decade,"I think there has been,until recently,a sense of frustration and some fatalism China has essentially got de facto control of the South China Sea and there isn’t much the world can do.

The international community is beginning to see the South China Sea is not a lost cause.

"But China’s comprehensive alienation of so many countries this year,and its determination to press ahead with maritime bullying even under the cover of the pandemic,these factors have begun to embolden a wider range of countries. What's really important is that several south-east Asia countries have been more emboldened in the last six months.

"Malaysia,Indonesia and Vietnam have all started pushing back,with different levels of assertiveness,and the international community is beginning to see the South China Sea is not a lost cause."

The"grey zone"in the South China Sea has,arguably,never been hotter.

Why does it matter to Australia,and what are we doing?

The contest over the South China Sea may seem a step removed from Australia's immediate national interests,but nothing could be further from the truth. What happens in the months and years ahead will be enormously consequential for Australia as a free and open,trade-exposed nation.

Were China to gain mastery of the seas,for example,it would have the ability to shut down global trade between nations with which it was in dispute – for example,LNG exports from Australia or Qatar to Japan could be squeezed.

Fishing stocks in the sea are under growing pressure,too,which has a potential knock-on effect on third countries looking to expand their fishing south towards Australian waters.

Australia regularly sails through the waters and,as recently as July,five vessels were confronted by Chinese navy ships in the disputed waters.

And then there's power projection. China's air force and navy are steadily growing in size and capability. The islands buttress those capabilities,allowing deeper power projection throughout the region via its cruise missiles,bomber and fighter jets.

Unlike the US,Australia's well-equipped – but comparatively tiny – navy doesn't conduct FONOPs within the 12 nautical mile zone of China's islands in the sea.

But it does regularly sail through the waters and,as recently as July,five vessels were confronted by Chinese navy ships in the disputed waters. The confrontation was handled in a"safe and professional"manner,according to the Defence Department.

Australian Poseidon aircraft,forward deployed to Royal Malaysian Air Force Butterworth,also regularly conduct surveillance missions in the South China Sea. Though it's rarely discussed by either nation,this surveillance – dubbed Operation Gateway – also provides useful intelligence about activity in the South China Sea.

The ANU's Medcalf says that Australia does"quite a lot already"in the South China Sea and shouldn't rush into conducting FONOPs within the 12 nautical mile zone,despite pressure from some China hawks to do so.

"I think it's important that Australia indicates it reserves the right to conduct FONOPs within 12 nautical miles,it is our right to do so,but I don’t think that automatically means that we have to do it."

As Blaxland says,"The key thing is about presence,about not conceding China's claim. It’s about maintaining the position that China's nine-dash line is not recognised,to avoid it being de facto recognised. And this is becoming more important as China becomes more aggressive and as its position with the manufactured islands has become more established."