Understanding the Senkaku/Diaoyu Islands Dispute: Diplomatic, Legal, and Strategic Contexts

E-International Relations | Yoichiro Sato, Astha Chadha

Japan continues to maintain de facto administrative control over the uninhabited Senkaku Islands, which are located 190 nautical miles off Okinawa, despite intensifying operational friction with the People's Republic of China Coast Guard. Beijing asserts sovereignty over the feature, known in China as Diaoyu Dao, citing historical Ming and Qing dynasty maritime records.

Hydrocarbon surveys conducted in the late 1960s transformed the quiet maritime boundary into an active strategic flashpoint. Japan bases its legal claim on the 1895 incorporation of terra nullius territory, whereas China claims the islands were improperly ceded under the 1895 Treaty of Shimonoseki. Tensions spiked following Tokyo's nationalization of the islets in September 2012. Sovereignty remains unyielding. Consequently, Japan has strengthened its independent maritime assets while actively lobbying Washington to reinforce security guarantees under the US-Japan bilateral alliance, even as Beijing attempts to isolate the United States from the dispute.

Comment

Beijing's persistent deployment of China Coast Guard vessels into the territorial waters of the Senkaku Islands directly probes the ambiguous thresholds of Article 5 of the 1960 US-Japan Mutual Cooperation and Security Treaty. While Washington has repeatedly confirmed that Article 5 covers territories under Japanese administration, civilian-led maritime intrusions create an operational dilemma below the threshold of an armed attack. This grey-zone posture complicates Tokyo's reliance on American military deterrence by forcing the Japan Coast Guard to absorb operational friction without escalating to Joint Self-Defense Force deployment.

A comparable operational dynamic exists around Second Thomas Shoal, where Chinese maritime militia and coastguard units test the boundaries of the 1951 US-Philippines Mutual Defense Treaty. By keeping pressure below the kinetic threshold that obligates direct American military intervention, Beijing systematically degrades the administrative authority of Washington's regional partners. Consequently, the deterrence framework of the 1960 US-Japan treaty faces a structural challenge from non-kinetic grey-zone maneuvers rather than conventional naval surface combatants.

Strategic Question for Discussion

If China Coast Guard incursions near the Senkaku Islands remain below the threshold of an armed attack, does Article 5 of the 1960 US-Japan treaty retain its deterrent value, or does it shift the operational burden entirely onto the Japan Coast Guard?

The pattern suggests that Article 5 successfully deters full-scale kinetic seizure by the People's Liberation Army Navy, yet offers limited leverage against incremental grey-zone tactics. My assessment is that this operational dynamic forces Tokyo to rely on the Japan Coast Guard for daily presence while continuously requesting public reaffirmations of the 1960 treaty from Washington. Over time, this arrangement risks taxing Japanese maritime law enforcement capabilities without establishing a definitive operational counterweight.

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