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

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 are compatible in terms of economy, military, and diplomacy. Vietnam’s post-1991 turn to the sea entails the development of a maritime economy, the modernization of its navy and air force, and the peaceful settlement of the South China Sea disputes via international arbitration. Likewise, Japan’s FOIP, first laid out in 2007, emphasized the securing of sea lanes stretching from the Indian Ocean to the Pacific Ocean for economic exchanges. Its 2010 National Defense Program Guidelines called for a new “dynamic defense force” away from Cold War-era style equipment and organizations capable of responding to threat from the southwest, and its 2013 National Security Strategy opposed any unilateral attempts to change the status quo in the East and South China seas in violation of international law. Japan-Vietnam joint statements show an evolution of compatibility in their respective grand strategies. Before China submitted its “nine-dash line” map to the United Nations in 2009, Japanese and Vietnamese leaders did not emphasize maritime security in their joint statements, although there were low-level defense exchanges. Statements released by both sides in 2007 and the 2008 did not mention maritime cooperation at all, and economic cooperation was the main topic of discussion. After Beijing’s move, however, maritime cooperation became one of the key tenets of bilateral ties. Tokyo and Hanoi incrementally discussed maritime cooperation as a measure to safeguard regional peace in joint statements issued in 2010 and 2011. The 2014 joint statement mentioned maritime security as an area of cooperation for the Vietnam-Japan partnership, the same year Japan provided Vietnam six vessels and one year after Japan protested China’s declaration of an Air Defense Identification Zone over the East China Sea. The 2015, 2018, 2023, and 2025 joint statements likewise underlined the importance of maritime security. A joint grand strategic focus on maritime security has also guided Japan’s provision of economic aid and military equipment to Vietnam. Japan wants to boost Vietnam’s economic resilience in case of Chinese economic retaliations against Vietnam’s assertion of its maritime claims. Japan’s ODA has helped Vietnam strengthen its manufacturing capability and lessen Vietnam’s need for Chinese investment under Beijing’s Belt and Road Initiative. It has also pledged to deepen cooperation over energy, critical minerals, semiconductors, supply chains, and artificial intelligence. Japan’s transfer of naval technology, platforms, and expertise to Vietnam serve to secure the South China Sea sea lanes and the flow of oil from the Middle East to Japan. The recent proposal to jointly develop fast landing crafts indicates Japan’s support for Vietnam holding and possibly retaking offshore islands. Defense cooperation is poised to go upward as Japan expands its OSA budget. In terms of diplomacy, Japan’s frequent calls to Vietnam’s ports help build a consensus and expectations for future U.S. port calls. Major U.S. Navy visits to Vietnam’s ports are often preceded by Japan Maritime Self-Defense Force (JMSDF) visits. Closer Japan-Vietnam diplomatic ties also allow Japan to augment its relations with ASEAN. Japan’s opposition to unilateral changes in the South China Sea supports its case for condemning China’s assertiveness in the East China Sea. Although Japan is not a great power and cannot defend Vietnam due to legal and material constraints, Vietnam welcomes close maritime cooperation with Japan, which helps to strengthen Vietnam’s multilateral foreign policy. Japan’s constitutional constraints on fighting overseas wars have meant that Vietnam can evade the stigma of siding with one country against another, which is a principle of Hanoi’s Four Nos doctrine. Moreover, Tokyo’s economic and military assistance do not carry any conditions on human rights or pose a threat to the political authority of the Communist Party of Vietnam to the degree of those from the West. Importantly, a close relationship with Japan prevents Tokyo from seeing Hanoi’s island reclamation activities as a threat to its sea lines of communication the way it sees Beijing’s activities. Vietnam supports Japan becoming a permanent member of the United Nations Security Council, a position that China opposes. So long as Japan’s and Vietnam’s grand strategies align over the South China Sea, bilateral ties will continue to improve. There are still grounds for an expansion of cooperation. Currently, the Vietnam People’s Navy and the JMSDF spearhead defense cooperation. Their land forces have not played much role. Japan should consider supporting Vietnam’s objective in the continental domain, such as boosting Hanoi’s land infrastructure to tighten connectivity with Laos and Cambodia to lessen the two countries’ dependence on Chinese investments, exchanging views on how to use land forces to fight a maritime conflict, and developing weapons that are suitable for both continental and maritime domains such as missiles, drones, and radars. Japan’s assistance to Vietnam address the maritime-continental dilemma and move beyond a purely maritime focus will elevate Japan-Vietnam ties to an even higher ground.