For decades, Beijing has sought to co-opt and lure its Southeast Asian neighbors into acquiescence with its maritime expansion through a package of economic incentives, military intimidation and a diplomatic charm offensive.
But now major regional countries have begun to assert their sovereign rights with greater resolve. In the past three months alone, Indonesia, Malaysia and Vietnam have challenged China's expansive maritime claims and coercive intrusion into their waters -- with significant effects on the geopolitical balance of power.
Following a monthslong naval standoff over the energy-rich Vanguard Bank sandbar last year, Vietnam has threatened China with international legal arbitration. In November, Vietnamese Deputy Foreign Minister Le Hoai Trung warned his country was considering options for defending its legitimate interests and challenging the legal basis of Beijing's claims, which cut well into smaller neighbors' exclusive economic zones.
In particular, Hanoi has been encouraged by the precedent set with the Philippines' successful arbitration ruling in 2016, which nullified and rejected China's "nine-dash line," undermining its claims in the South China Sea and its alleged "historic rights." China then had to drop the term from its formal statements and search for alternative legal doctrines and documents to support its shaky claims.
As the current chair of ASEAN, Vietnam is a unique position to advocate for a tougher diplomatic censure of China's disruptive behavior against smaller neighbors.
Given its de facto alliance with the U.S. in recent years, which now includes large-scale defense cooperation and military aid, Vietnam could more openly call on external powers to assist regional efforts to constrain China's aggression.
In fact, Hanoi played this role almost exactly a decade ago, when it successfully encouraged the Obama administration to challenge China's threats to freedom of navigation in the South China Sea.
Shortly after Vietnam's legal threats, Malaysia forged ahead with a bolt from the blue legal challenge to China. The country, which has historically maintained warm relations with Beijing, made a submission -- prepared in 2017 -- to the U.N., claiming a greater share of the continental shelf, which cuts well into China's claims over the Spratly Islands and central portions of the South China Sea.
The submission, which was likely prepared shortly after the Philippines' arbitration award, was postponed while Prime Minister Mahathir Mohamad, who came into power in 2018 on the back of simmering anti-China sentiment, focused on limiting his country's debt exposure to big-ticket Chinese infrastructure projects.
But once he secured major adjustments and discounts to Chinese projects, the maverick leader has subsequently switched to challenging Beijing's intrusion into its EEZ and traditional waters. Foreign Minister Saifuddin Abdullah has characterized China's excessive claims in the area as "ridiculous."
Perhaps the most dramatic and significant response has come from Indonesia, Southeast Asia's largest nation and presumptive leader. In a departure from its age-old "whisper diplomacy," avoiding open confrontation with a major economic partner, Indonesia has now formally questioned the legality of China's claims and bolstered its military position close to the contested area.
Indonesia has experienced a dramatic increase in the number of Chinese paramilitary and illegal fishing vessels off the coast of the resource-rich Natuna Islands, which overlap with the tip of China's nine-dashed-line. Initially, Indonesia adopted an aggressive "Sink the Vessels" policy, which targeted dozens of illegal Chinese boats.
There are three consequences of this toughening stance in the South China Sea. First, it underscores the fragility of China's policy of winning over regional elites and its economic largesse there. Regional leaders, even those overly friendly to China, have come under intense public pressure to stand up to a revanchist Beijing.
In Vietnam, popular nationalism, long anchored by opposition to Chinese aggression, has been reinforced by festering disputes in the South China Sea. Meanwhile, in Muslim societies such as Indonesia and Malaysia, anti-Chinese sentiments have been exacerbated by Beijing's persecution of Uighur Muslims in Xinjiang.
Bottom-up anti-China pressure on regional leaders will only increase if Beijing continues its current course.
Second, it signals ASEAN's growing resistance to any pact which would undermine the strategic interests and sovereign rights of neighboring countries. This is relevant given negotiations over the China-ASEAN Code of Conduct in the South China Sea, which are set to be concluded by 2021.
Finally, we are likely to see deeper, albeit surreptitious, defense cooperation between core ASEAN nations and major external powers such as the U.S., Japan and India.
The U.S. and like-minded powers have stepped up joint naval exercises, intelligence-sharing and defense aid for regional states such as Vietnam and Indonesia, which are rapidly developing their own maritime security capabilities. Under Mahathir's leadership, ASEAN will assert its centrality and autonomy from Chinese influence.
China is discovering that it cannot simply buy the silence and submission of its neighboring countries through economic investments alone. If anything, its unabated maritime expansionism has hardened resistance, pushing them into the embrace of external powers that wish to check Beijing's worst instincts.
Richard Heydarian is an Asia-based academic, columnist and author of "The Rise of Duterte: A Populist Revolt Against Elite Democracy" and the "The Indo-Pacific: Trump, China and the New Struggle for Global Mastery."