So as best I can gather and understand, here is what happened and what it means (THREAD): https://twitter.com/Reuters/status/1282775563527237633

China has made various territorial assertions in the South China Sea which the US has "objected" to in the past, but not formally "rejected", leaving the door open (in principle) to some reconciling formula, however unlikely.

The boldest Chinese claim is the Nine Dash Line, asserting a sovereign claim over most of the South China Sea. Though it insists on putting the Nine Dash Line on maps, my understanding is that China has been somewhat coy about asserting this claim formally and explicitly.

The US has never accepted the Nine Dash Line as a valid claim, but neither has it explicitly rejected it, in part because China has not formally asserted it.

Then there are territorial claims to specific islands in the South China Sea, which China also claims gives rise to claims on the waters surrounding those islands. This gets complicated.

UNCLOS (UN Convention on the Law of the Sea) is a treaty that the US signed but the US Senate never ratified, but the US adheres to in principle. China, on the other hand, is a party to the treaty.

UNCLOS says that any coastline, including islands, gives rise to a traditional 12-mile limit of territorial waters that belong to that country, as part of its sovereign territory. It has exclusive rights and full control over who can enter, transit, or leave.

UNCLOS also says that any coastline, including islands, also give rise to a 200-mile Exclusive Economic Zone (EEZ) over which that country exercises exclusive rights to the resources, such as fishing or mining.

China claims that it owns certain islands and features in the South China Sea. In many cases, other countries, such as Vietnam, the Philippines, and Malaysia, claim them as well.

The US has previously taken an agnostic view on these conflicting claims per se, saying only that the conflicts should be worked out peacefully.

But China also asserts that, in addition to the 12-mile territorial waters these island claims create, they also give rise to a 200-mile EEZ. And that EEZ, China claims, are also territorial waters which it has the right to control, and restrict movement through.

The US disagrees with this interpretation of an EEZ, arguing that where one does exist, it is a zone recognizing rights of economic exploitation (fishing, mining, oil drilling) alone. For purposes of transit of, say, US Navy warships, an EEZ is international waters.

But there's also a question of whether the reefs, shoals, and islets in the South China Sea, which China and others claim, actually give rise to an EEZ. If they are "islands", they do, but ...

In 2016, the Philippines brought a case against China in the Permanent Arbitration Court in the The Hague, over China's naval occupation of Scarborough Shoal, a fishing ground the Philippines had long claimed as its own.

China raised a huge fuss over the Philippines even bringing the case, and refused to participate or accept the ruling.

But the Philippines won its case. The Court ruled that China had no valid historical claims under the Nine Dash Line, and - just as important - that legally none of the islets in the Spratly Islands qualified as "islands" but just "rocks".

If you own a "rock" in the ocean, it gives rise to a 12-mile territorial waters claim. But it does NOT give rise to a 200-mile EEZ, under UNCLOS. So that meant China had no claim to an EEZ, even a purely economic one, based on its land claims in that part of the South China Sea.

China rejected the ruling. So, interesting enough, did Taiwan, which as the "Republic of China" shares and supports China's national claims to the South China Sea, and occupies at least one islet there.

Then there's the issue of manmade islands. China has been landfilling reefs in the South China Sea into larger islands that house military bases and airfields. But according to UNCLOS, creating artificial islands does not create ANY maritime claim, either 12-mile or EEZ.

So ... that's a lot of complicated background. What does the new State Department statement mean?

First of all, it explicitly sides with the Philippines and the Arbitration Court over Scarborough Shoal. The US has already implicitly sided with the Philippines, sending US naval ships to the area, bolstering the Philippine navy, and warning China not to attack them.

But this statement makes it more explicit that the US formally rejects China's claim and accepts the court's ruling (which China angrily rejects) in favor of the Philippines, perhaps laying the foundation for more assertive US actions.

Second, the statement aligns itself with court's ruling that China's claims to islets in the Spratlys (which the US doesn't necessarily reject) are not islands and do not give rise to any EEZ claim beyond the 12-mile territorial waters limit.

In the absence of the Nine Dash Line, this severely circumscribes any Chinese claim to sovereign rights over the bulk of the South China Sea, beyond a few very small islets and their immediate surroundings.

The US also explicitly rejects the Nine Dash Line. This is not a substantive change from the previous US position, but it's more explicit and final.

And then finally, the US names one disputed feature, the James Shoal, which is located just off the northern shore of Borneo, and rejects China's claim in favor of Malaysia.

The James Shoal is already effectively administered by Malaysia, which is involved in undersea oil exploration there. China has sent a few naval ships there from time to time, mostly for symbolic purposes.

James Shoal is notable because it is the southernmost feature within the Nine Dash Line, so represents the "furthest extent" (and least tenable) of China's maritime claims.

So is any of this important? It depends. The statements themselves represent an evolution, rather than a sharp break from, prior US policy towards the South China Sea. It makes certain positions which the US has implicitly held for many years more open and explicit.

It potentially lays the legal foundation for the US to take more assertive action contesting China's efforts to control, and interfere with other countries activities, in the South China Sea ... if it wishes and is prepared to do so.

The real question is, what is the US prepared to do, where, and alongside whom?

Up to this point, under both Obama and Trump, US action has mainly consisted of sending US Navy ships on "freedom of navigation" transits through the South China Sea to assert that our position that they are (for the most part) international waters.

We have also interacted with ASEAN members to express our shared concerns and call on China to establish and obey some "rules of the road' in disputed areas. (When Hillary Clinton did this very explicitly, it made China furious.)

The Trump Administration has taken some action to bolster the Philippine's previously rather small navy, as well as warn China against a confrontation with the Philippines. But Duterte's often mercurial nature complicates our ability to rely on the Philippines as a partner.

Meanwhile, China continues to develop its artificial islands and military bases in the South China Sea, with neither Obama or Trump apparently willing to take the risk of any serious action to stop them.

So the real thing to watch here aren't words, but actions. Will the US take a more active role in counter-policing disputed areas of the South China Sea? Where, and alongside whom? What would China's response be? Does it meaningfully change the balance of control?

Thanks for following a lengthy and somewhat complicated thread. I'm sure some of you with subject expertise may correct a few of the points I have made. I take no offense.