In the past few days, China has launched a broad and well coordinated media campaign to express opposition to the Japanese government’s purchase of three of the While tensions rise between Japan and China in the East China Sea, an important development may have been overlooked.

(Diaoyu) Islands from a private Japanese citizen.  The campaign has included remarks by almost every member of the Politburo standing committee, an authoritative statement by the Ministry of Foreign Affairs and semi-authoritative commentaries in official media sources such as thePeople’s Daily, PLA Daily, and Xinhua.

Nevertheless, amid all the expressions of indignation, one of the most important elements of China’s response has been overlooked: agovernment statement announcing baselines to demarcate China’s territorial sea around the disputed islands.  Under the UN Convention on the Law of the Sea, a state enjoys the equivalent of territorial sovereignty within this zone, which extends 12 nautical miles seaward of the baselines that a state declares.

When China first declared its baselines in 1996, it did not publish base points for three areas that were under dispute: the Spratly Islands in the South China Sea, Taiwan, and the Senkakus.  China did draw baselines around the Paracel Islands, which Vietnam claims, but likely did so because it had controlled the entire archipelago for several decades.

At first glance, the announcement of baselines around the Senkakus might just be a symbolic declaration of sovereignty that will not change any facts on the ground.  Although China could not prevent the sale of the islands, the media campaign has emphasized that this act does not alter China’s claims, a point that the baselines underscore.

Nevertheless, beyond re-affirming China’s claims, the announcement of baselines may matter for several reasons.  First, from China’s perspective, it establishes a legal basis for China’s claim to jurisdiction not just over the islands but also, more importantly, over the waters around the islands.  On September 13, China submitted its baselines to the United Nations in accordance with UNCLOS.

Second, as a result, it creates a rationale for an increased Chinese presence around the islands.  The importance of this rationale was revealed on September 14, when the Ministry of Foreign Affairs announced that two task forces with a total of six ships from the China Marine Surveillance Force had been dispatched to the waters near islands to “defend our maritime rights and interests.”

Third, a struggle between Chinese and Japanese government ships may occur to control the 12 nautical mile territorial sea around the islands.  In the past, Chinese vessels have usually respected this line, though it has occasionally been crossed temporarily to underscore China’s claims.  If cooler heads fail to prevail, however, the increased number of ships in the area, seeking to exercise control over the territorial sea around the islands, could spiral out of control in ways that neither country wants.  Hopefully cooler heads will prevail.

[This originally appeared in The Diplomat.]