The Gray Zone in the Definition of Gray-Zone Warfare: Challenges for Japan-U.S. Cooperation
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The Gray Zone in the Definition of Gray-Zone Warfare: Challenges for Japan-U.S. Cooperation

by Hideshi Tokuchi
May 25, 2021

This essay examines the differences between the Japanese and U.S. definitions of “armed attack” and “gray zone,” discusses Chinese gray-zone activities in the East China Sea around the Senkaku Islands, and considers options for the two allies to address this evolving threat.



China’s approach to asserting its claim over the Senkaku Islands through gray-zone activities seems intended to circumvent the U.S. defense commitment under the Japan-U.S. Security Treaty. As a result, the concept of “gray zone” must be understood so as not to block alliance cooperation to achieve common security goals. Gray-zone warfare violates the sovereignty and national interests of foreign countries in a manner that does not rise to the level of armed attack. The challenge for Japan and the U.S. is how to effectively cooperate with each other outside the commitment of Article 5 of their security treaty. Given the allies differing interpretations of the term “armed attack,” they should devise a practical way for operational cooperation, including coordination of their rules of engagement. With the rapid development of the China Coast Guard and China’s problematic new Coast Guard Law, cooperation to address China’s gray-zone warfare has become even more pressing for the Japan-U.S. alliance.

  • Japan and the U.S. must not be complacent about the current robustness of the alliance but should squarely face the security challenge that China has been posing, particularly in the East China Sea.
  • The allies need to develop a better understanding of each other’s relevant security institutions, regulations, and processes.
  • A whole-of-government and whole-of-alliance approach must be pursued under the strong political leadership of the two countries.

Hideshi Tokuchi is a Visiting Professor at the National Graduate Institute for Policy Studies (GRIPS) in Tokyo.