Context. Japan is a U.S. treaty ally and a major U.S. strategic partner in the Indo-Pacific. When Chinese military aircraft enter Japanese airspace without authorization, the Japanese air force sends fighter jets in response. The frequency of Chinese incursions into Japanese air space reflects tensions between China and Japan and the aggressiveness of China's foreign policy. For example, the spike in 2016 coincided with Japan's announced intention to revise its constitution in a manner China found threatening (Gui Yongtao).

Data and resolution details. This question resolves in April 2021 based on official figures released by the Japanese government (Japan Air Self-Defense Force).

The data underlying the graph is here.

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Issued on 11/02/20 03:53pm
Japan's "territorial airspace" is not the same as its "Air Defense Identification Zone" (ADIZ). Japan's air force typically scrambles jets in response to violations of its ADIZ, which it views as threats to its territorial airspace. This question resolves based on what Japan's Ministry of Defense reports as scrambles in response to "aircraft intruding into Japan's territorial airspace," regardless of whether the intrusion was in fact of Japan's territorial airspace. See, e.g., https://www.mod.go.jp/js/Press/press2020/press_pdf/p20200409_02.pdf