Japan-India Defense in a Fragmenting Indo-Pacific

At their late-August summit, former Prime Minister Shigeru Ishiba and Indian Prime Minister Narendra Modi adopted a suite of documents signaling their nations’ intent to increase cooperation across security and economic domains. Chief among these was the “Japan-India Joint Vision for the Next Decade”, a state-level agreement by the two leaders outlining a 10-year roadmap for bilateral cooperation.

Yet this agreement comes at a moment of heightened uncertainty for India. Since May, New Delhi’s relations with Washington have deteriorated sharply, eroding India’s international position and placing unprecedented strain on “the Quad,” a diplomatic partnership between Japan, India, Australia and the U.S. committed to fostering a free and open Indo-Pacific.

The once-routine Quad leaders’ summit in New Delhi, planned for this autumn, wasn’t held — raising fundamental questions about how a “half-cracked” Quad will shape Japan-India defense cooperation in the decade ahead and how Tokyo should respond.

Long perceived as enjoying a period of close personal and diplomatic alignment, U.S.-India relations deteriorated rapidly following disagreements over the India-Pakistan conflict and Washington’s imposition of punitive tariffs on Indian goods.

The Trump administration’s decision to court Pakistan — India’s principal adversary — had already shaken New Delhi’s confidence. Whether this shift represents a tactical deviation or a long-term recalibration of U.S. regional strategy will require close monitoring.

Adding to the pressure, the forthcoming U.S. National Defense Strategy is expected to prioritize homeland and Western Hemisphere defense, implying a relative downgrading of Indo-Pacific deterrence. For India — which faces China on land in the Himalayas and at sea in the Indian Ocean — a diminishing U.S. presence risks emboldening China and narrowing India’s strategic space, with downstream implications for Tokyo’s efforts to deepen cooperation with New Delhi.

In contrast to worsening U.S.-India dynamics, China-India ties have shown signs of tactical improvement. Following the deadly 2020 clash in Kashmir, Indian business-sector pressure pushed its government toward dialogue, culminating in Chinese leader Xi Jinping describing bilateral ties as a “Dragon-Elephant Tango” during the 75th anniversary of diplomatic relations in April.

But beneath this veneer of detente lie deep strategic frictions. Modi reaffirmed in August that peace and tranquility at the disputed border is an “insurance policy” for stable relations. India remains especially concerned about Chinese military advances on the Doklam Plateau — a tri-junction area with India and Bhutan that overlooks the Siliguri Corridor, the narrow land bridge linking the North Eastern Region of India (NER) to the mainland.

Should the People’s Liberation Army (PLA) consolidate control there, China could sever the corridor with relative ease, effectively isolating the NER. Concessions reportedly made by India during recent negotiations have fueled criticism that New Delhi is walking into Beijing’s strategic trap. With Russia — India’s traditional partner — now drawing closer to China due to the war in Ukraine, India has diminishing room to maneuver and must maintain a delicate balance to avoid being strategically outpaced.

All this is putting great strain on the Quad diplomatic partnership. The original Quad faltered in the 2000s, but the grouping’s revival in 2017 was driven by shared concerns over China. Today, however, widening U.S.-India differences once again threaten to unravel the Quad. While potential improvements in U.S.-India ties and prospects for an early-2026 summit offer modest optimism, the overall trajectory remains uncertain.

For Tokyo, sustaining India’s participation is strategically vital — not only for Indo-Pacific balance-of-power considerations, but also for building China-resilient semiconductor and critical-minerals supply chains. Moreover, as India becomes more hesitant to rely solely on the U.S., its incentives to deepen cooperation with middle powers such as Japan will only increase. The Quad’s current fragility thus heightens — rather than diminishes — the strategic logic for robust Japan-India partnership.

Despite the growing importance of bilateral ties, India has always been reluctant to frame the Quad as an explicit mechanism for deterring China. India’s primary security challenge remains the land border with the Asian giant, limiting the relevance of maritime-focused Quad activities. While this year’s Malabar exercise in Guam signaled continued coordination between the navies of India, the U.S., Japan and Australia, substantive multilateral military deterrence is more likely to emerge through other groupings such as “the Squad” (Japan-U.S.-Australia-Philippines).

This makes bilateral Japan-India cooperation — especially in defense technology — both essential and feasible. India, having lost territory to China equivalent to the size of Kyushu during the 1962 border war, remains adamant that national defense must rely on indigenous capability rather than alliance guarantees. Japanese cooperation in defense R&D and production can elevate India’s long-term deterrence posture while imposing additional strategic costs on China — similar to how India’s export of BrahMos missiles is reshaping the Philippines’ defense calculus.

The North Eastern Region of India’s security challenges are also intertwined with broader economic and geopolitical stakes. The NER — culturally distinct but increasingly central to India’s “Act East” agenda — includes Arunachal Pradesh, which China claims as its own. Japan has major supply-chain interests in this region, including Tata’s large semiconductor facility under construction in Assam. Any escalation involving China would therefore carry direct implications for Japan’s economic security.

India’s ongoing military modernization — including plans for a nuclear-powered aircraft carrier and its diversification of defense partners away from Russia toward the U.S., France and Israel — creates new openings for Japan’s defense industry. Seizing these opportunities will require calibrated, demand-driven engagement rather than one-sided offerings.

Over the next decade, Japan-India defense cooperation must be grounded not in Japanese aspirations alone, but in India’s actual strategic needs. As the Indo-Pacific enters a period of sharper great-power rivalry, a “half-cracked” Quad and India’s geopolitical uncertainty make deeper bilateral cooperation both more urgent and more mutually beneficial.

In this midst of this shifting geopolitical landscape, one thing is certain: An effective Japan-India partnership will require sustained political alignment, targeted defense-technology collaboration and a shared commitment to stabilizing an increasingly contested strategic environment.

(Photo Credit: The Asahi Shimbun / Getty Images)

[Note] This article was posted to the Japan Times on Dec 9, 2025:

https://www.japantimes.co.jp/commentary/2025/12/09/japan/japan-india-defense-in-the-indo-pacific/

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