ASEAN Beat | Diplomacy | Southeast Asia

Grand Strategic Compatibility: The Basis of The Japan-Vietnam Partnership

The quick pace of reconciliation between Tokyo and Hanoi since the end of the Cold War has reflected the compatibility of their respective grand strategies.

Japanese Prime Minister Takaichi Sanae meets with Vietnam’s President and Communist Party chief To Lam, in Hanoi, Vietnam, May. 2, 2026.

In an address to Vietnam National University in Hanoi in May, Japan’s Prime Minister Takaichi Sanae affirmed Japan’s commitment to the Free and Open Indo-Pacific (FOIP) concept. Tokyo pledged to increase its political, economic, and defense cooperation with ASEAN so that each ASEAN state can “acquire autonomy and resilience” in the face of intensifying geopolitical competition. It was Takaichi’s first public address on updating her predecessor Abe Shinzo’s FOIP vision, and her decision to deliver it in Vietnam says a lot about the current state of Japan-Vietnam ties.

The reconciliation between Japan and Vietnam since the end of the Cold War has been nothing short of extraordinary. During the Third Indochina War (1978-1991), Japan sided with China and the United States to isolate Vietnam due to its status as a Soviet ally. Japan’s alignment was rooted in its fear of a Soviet invasion from the north in the late 1970s. Beginning in May 1978, Moscow had increased the number of troops stationed on Soviet-controlled Southern Kuril Islands up to 6,000. The Soviets also built up their Pacific Fleet until it became the largest of the four Soviet fleets, and they deployed the SS-20 intermediate-range ballistic missiles to the Asia-Pacific theater.

Consequently, Japan signed a Treaty of Peace and Friendship with China in August, which included an anti-hegemony clause implicitly directed against the Soviet Union. Japan strengthened naval cooperation with the United States and participated in the Rim of the Pacific Exercise for the first time ever in 1980. It also built up its own navy and air force to balance against the Soviet threat and hedge against the possibility of the U.S. retrenchment from the Asia-Pacific. The goal was to protect not only the home islands but also the sea lines of communication up to 1,000 nautical miles from Japan’s coasts.

Japan had provided economic aid to Vietnam between 1975 and 1976 to help it recover from the Second Indochina War, but after Hanoi formally allied with Moscow in November 1978 and invaded Cambodia to topple the Khmer Rouge in December, Tokyo quickly froze aid. It then failed to condemn China’s retaliatory invasion of Vietnam a few months later. In April 1979, Japan conditioned the resumption of economic aid to Vietnam on Hanoi not establishing permanent Soviet military bases in Danang and Cam Ranh Bay, which Japan worried would threaten the supply of oil from the Middle East. As Vietnam proceeded to host Soviet armed forces and occupied Cambodia during the 1980s, Japan added another condition to aid resumption, which was Vietnam’s troop withdrawal from Cambodia. Japan didn’t resume aid until 1992, after the Soviet collapse and the signing of the Paris Peace Agreements on Cambodia.

Since then, Japan’s Official Development Assistance to Vietnam has totaled approximately $29.3 billion, the largest of any Vietnam’s foreign donors. Japan is Vietnam’s third largest investor and fourth largest trading partner. Both countries began low-level defense exchanges around the same time with agreements reached over Japanese ships’ port calls in Vietnam, joint search-and-rescue operations in the South China Sea, and training of Vietnamese students at Japan’s National Defense Academy. In 2014, Japan agreed to provide Vietnam with six used vessels and six years later with technologies for building military ships to boost Hanoi’s maritime capability. In 2021, Japan signed an agreement with Vietnam to allow for the transfer of defense equipment and technology.

Vietnam falls under the scope of Japan’s new Official Security Assistance under the 2022 National Security Strategy. In 2026, Tokyo lifted a ban on the export of lethal weapons, which would allow it to sell fighter jets, missiles, and warships. Unlike with other Asian countries, the issue of Japan’s crimes committed during World War II do not cloud bilateral relations with Vietnam. The country is now one of the most pro-Japan countries in Asia. Vietnam established a partnership with Japan in 2002 and later a strategic partnership in 2009. Vietnam elevated Japan to the status of a Comprehensive Strategic Partner in 2023.

The quick pace of Japan-Vietnam reconciliation has to do with the compatibility of their respective grand strategies. During the Third Indochina War, Vietnam prioritized western and northern Indochina over the South China Sea, while Japan was occupied with defending against a Soviet invasion from the Southern Kurils. There was little cooperation during this period. After the Third Indochina War, Hanoi and Tokyo shared the same concerns over China’s contestation of their respective maritime sovereignties. Vietnam began to look east to the sea while Japan slowly pivoted to the southern islands and considered maritime zones outside of Northeast Asia vital to its security. In this context, Japan supports the combination of the East China Sea and the South China Sea into a single theater of operation.

Political leaders from both countries began to develop grand strategic visions that........

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