In Hanoi on September 10, 2023, US President Joe Biden and the General Secretary of the Communist Party of Vietnam Central Committee Nguyễn Phú Trọng upgraded their countries’ diplomatic relationship to a “comprehensive strategic partnership” (White House, September 11). Vietnam bestows this term on the countries with which it has the highest level of diplomatic cooperation. The move surprised many, as did Biden’s prioritizing of the visit over the ASEAN summit the same day (Nikkei Asia, September 7). The United States had spent the last decade at the lowest level—a “comprehensive partnership.” This latest development puts the United States on a par with China, with whom Vietnam shares a communist ideology and on whom Vietnam is heavily economically dependent (Asia Times, February 2). This was thus a watershed moment for two countries that have not forgotten their fraught past.
While US policymakers welcome the diplomatic achievement, close observers note that Vietnam’s actions remain driven by its relationship with China. Even the recent upgrade in relations with the United States was “carefully crafted” to ensure that Vietnam did not antagonize China too directly.  Carlyle Thayer, a Vietnam expert and professor at the University of New South Wales Canberra, described Vietnam’s rationale for the diplomatic upgrade as stemming from its strategy of “cooperation and struggle” with China.  Former US Ambassador to Vietnam David Shear noted that the Vietnamese “place much more importance on their relationship with China than they do with the US because [China] is so close.”  While Vietnam has pursued a balancing strategy for decades, it has primarily tempered its engagement with the West according to the mood in Beijing. However, China’s overbearing posture in the South China Sea has now eroded much of the progress Sino-Vietnamese relations had made since the early 2000s.
The significance of Biden’s visit was presaged by a 2019 modification to Vietnam’s defense policy. That December, the Ministry of Defense issued a new white paper which changed a long-held policy of “Three Nos” to “Four Nos and One Depend,” a precise, if inelegant, moniker (AMTI, December 17, 2019). This followed a tense decade of diplomatic and maritime conflict over the sovereignty of economic and territorial rights in the South China Sea.
The Origin of Three Nos
China and Vietnam have a long history of strained relations. In 40 A.D., two Vietnamese sisters known as Trung Nhi and Trung Trac led a rebellion against their Chinese overlords in the territory that is now North Vietnam. Though ultimately unsuccessful, they became symbols of nationalistic pride in the country’s struggle against China, something which endures to the present. After successful communist revolutions in both countries and North Vietnam’s expulsion of the US and France, Sino-Vietnamese relations broke down in the 1970s due to Vietnam’s increasing reliance on the Soviet Union, which China saw as a geopolitical rival. In 1974, Chinese forces took advantage of a divided Vietnam to capture the crescent group of the Paracel islands, which they hold to this day. The two then fought a land border war in 1979 and a naval battle over Johnson Reef in the Spratly Islands in 1988. But after the fall of the Soviet Union as the center of the communist bloc, Vietnam was forced to reconsider its foreign policy alignments. In November 1991, China and Vietnam normalized diplomatic relations, though they clashed over maritime claims throughout the 1990s.
Vietnam had reason to hope relations were improving going into the 2000s, however. In 1999, the two signed a land border treaty, and in 2004, they signed a treaty demarcating the maritime border in the Gulf of Tonkin. In 2002, the Association of Southeast Asian Nations (ASEAN), of which Vietnam is a member, and China signed the Declaration on the Conduct of Parties in the South China Sea. The Declaration was conceived as a rhetorical commitment to establishing an eventual Code of Conduct which would be binding on all parties to avoid the use of violence in maritime disputes. Finally, in 2008 Vietnam upgraded its diplomatic relations with China to the status of a “comprehensive strategic partnership.”
Vietnam’s Ministry of Defense published three White Papers between 1998 and 2009 reaffirming three central tenets—no aligning with one country against another, no military alliances, and no hosting foreign military bases on Vietnamese territory—that became known as the “Three Nos.” This policy formed the backbone of Vietnam’s military diplomacy, simultaneously avoiding incorporation into a Chinese sphere of influence and placating the Chinese Communist Party (CCP) by constraining Vietnamese military engagement with the West. While the policy informed Vietnam’s interactions with all countries, the Three Nos was “designed to reassure the Chinese and fend off the Americans at the same time.” 
Changing Tides: China’s Territorial Creep
As early as 2009, however, China began to lay the groundwork for more assertive rhetoric and behavior in the South China Sea (SCS). In May, China submitted two notes verbale to the United Nations’ Commission on the Limits of the Continental Shelf (CLCS), which included a map of the SCS with nine very conspicuous dashed lines (United Nations, May 7, 2009). For the first time in official diplomatic channels, this map including China’s Nine-dash Line (断续线) appeared to lay claim to nearly 1.3 million square miles of sea. Shortly thereafter, China reportedly began to speak of the SCS as a “core interest,” suggesting to many that it was willing to defend its claim by force (Chinafile, February 22, 2011).  Negotiations with ASEAN toward a Code of Conduct stalled and progress to this day has been stymied due to increasing hostility in the SCS and China’s influence over some members of the Asian bloc.
Through the use of its maritime militia and coast guard, Chinese harassment of Vietnamese fishermen has increased in line with this rhetoric. Chinese coast guardsmen have boarded fishing vessels to assault fishermen, destroying their equipment or arresting them. They have intimidated unarmed civilians using water cannons and occasionally rammed and sank fishing boats or trawlers (BBC, April 8, 2011). One study cites 34 publicly reported law enforcement encounters constituting harassment between 2010 and 2019 (CSIS, August 18, 2016). In a particularly brazen attempt to exert sovereignty inside Vietnam’s Exclusive Economic Zone (EEZ), the Chinese oil rig Haiyang Shiyou (海洋石油, HYSY) 981 conducted oil exploration in May 2014, escorted by over 40 ships from the Chinese Coast Guard, Navy, and Maritime Militia. Vietnam chose not to back down, sending dozens of its own ships to compel the oil rig to withdraw, which culminated in a six-week stand-off (AMTI, June 12, 2017). Ultimately, China removed the rig. Vietnam hailed its victory, but the damage to Vietnam-China relations was done. Within two weeks, Vietnamese Deputy Prime Minister Pham Binh Minh called US Secretary of State John Kerry to discuss elevating bilateral ties and removing weapons embargos by the United States (Vietnam MOFA, July 1, 2014).
By 2016, China’s land reclamation activities in the SCS had placed military airports, seaports, and long-range missile systems on Fiery Cross, Subi, and Mischief Reefs. Combined with its established military outpost on Woody Island, China’s military reach now spanned nearly the entirety of the SCS, worrying other island claimants including Vietnam, the Philippines, Malaysia, and Brunei. This has all been made possible by a ballooning military budget, which one estimate puts at $298 billion this year—five times the figure in 2002 (CSIS, May 8). As the experience of Southeast Asian nations makes clear, China’s “peaceful rise” is anything but (NPC, July 1, 2011).
In response, the Vietnamese military began to change course. The fourth Ministry of Defense policy paper added a new provision against “using force or threatening to use force in international relations” (Radio Free Asia, November 27, 2019). The newly codified “Four Nos” policy contrasted Chinese aggression in the South China Sea with Vietnamese restraint. More notably, however, the military stated that “depending on circumstances and specific conditions, Viet Nam will consider developing necessary, appropriate defense and military relations with other countries on the basis of respecting each other’s independence, sovereignty, territorial unity and integrity.” Establishing a conditional policy provides more freedom of action for Vietnam’s military (AMTI, December 17, 2019). This supplementary clause gives Vietnam the room to deepen engagement with other partners and enhance its security position while avoiding China’s ire by preserving the original Three Nos.
Vietnam is diversifying its partnerships as tensions with China rise. In 2016, shortly after China placed long-range missile systems on islands in the Spratlys, Vietnam upgraded relations with India, a geopolitical rival of China, to the comprehensive strategic level (India Ministry of External Affairs, September 1, 2017). In 2022 and 2023, Vietnam upgraded its diplomatic partnerships with South Korea as well as with the United States, and has announced a future upgrade with Australia (Fulcrum, February 10; White House, September 11; VNExpress, August 22). The country is also reportedly on the cusp of a similar pronouncement with Japan (Yomiuri Shimbun, October 16).
Diplomatic hedging is simultaneously being buttressed in the military domain. In 2018, Vietnam hosted a US aircraft carrier for a port visit for the first time since the Vietnam war and sent delegates to the Rim of the Pacific Exercise (RIMPAC), the world’s largest multinational naval exercise, hosted by the United States. Chinese analysts have taken note, particularly of Vietnamese outreach to Japan (another state which disputes China’s maritime territorial claims) (The Diplomat, September 21, 2021).  In Japan, Vietnam’s shift in policy since 2019 is being described as “omnidirectional,” seeking to engage partners everywhere when interests are aligned, without committing to any particular bloc or ideology. 
Policymakers in the United States hail the diplomatic developments, but regional experts caution that Vietnam’s geographical context precludes a deeper embrace of the west: China and Vietnam share land and maritime borders, which is partly why Vietnam’s economy is highly reliant on Chinese exports.  Vietnam cannot fully break with China, nor is doing so in its strategic interests. Meanwhile, the United States is perceived to be an unreliable partner, not just for historic reasons, but due to the country’s divergent political system: In the eyes of Vietnam’s communist leadership, the United States’s democratic political processes result in erratic, short-term decision making. 
But the marked improvement in US-Vietnamese ties is positive for both countries, even if Vietnam is unlikely to categorically abandon its conciliatory approach towards Beijing. The Four Nos will be deployed with both Western partners and with China to provide Vietnam with some more autonomy. United States defense officials may find themselves frustrated by stalled progress on closer military integration as Vietnam calibrates its engagement with the West to its interest in placating China. Still, Vietnam’s shift to the less restrictive Four Nos policy is evidence of Vietnam’s stronger commitment to standing up in the face of China’s coercive tactics in the South China Sea, though that may also portend more skirmishes in defense of the country’s maritime claims.
 Thayer, Carlyle A., “Xi Jinping to Visit Vietnam – 2,” Thayer Consultancy Background Brief, October 11, 2023.
 Thayer, Carlyle A, “US-Vietnam Relations: Post Mortem – 5,” Thayer Consultancy Background Brief, September 13, 2023.
 David Shear, Former US Ambassador to Vietnam, interview by Author, April 3, 2023.
 Zack Cooper, American Enterprise Institute, interview by Author, April 28, 2023.
 Daozheng Wang, “Japan-Vietnam South China Sea Cooperation from the Indo-Pacific Perspective and Its Impact on China,” (印太视域下日越南海合作及其对华影响), Southeast Asian Studies 5 (2021): 75–92, https://doi.org/10.19561/j.cnki.sas.2021.05.075.
 Tomotaka, Shoji, “Vietnam’s Omnidirectional Military Diplomacy: Focusing on the South China Sea,” NIDS journal of defense and security, National Institute for Defense Studies, 2016, p.41-61.  Poling, Gregory, Center for Strategic and International Studies (CSIS), interview by author, May 9, 2023.