Thailand, the heavyweight economy of mainland Southeast Asia, has for the last two decades been a diplomatic lightweight.
On challenges such as the South China Sea, Myanmar or the prospect of a Chinese military presence in Cambodia, Thailand's voice has been inaudible. Although it is a U.S. treaty ally and cautious about getting too close to China, Bangkok's efforts at neutrality have in recent years looked more like paralysis.
But there are signs of life. Thailand is quietly seeking to shore up its waning economic and political influence in its immediate neighborhood. This area, which it calls the Mekong subregion, includes close neighbors Laos, Cambodia, Vietnam and Myanmar.
The renaissance of Thailand's Mekong ambitions began in 2018 when it hosted a low-profile summit under an unwieldy umbrella called Ayeyawady-Chao Phraya-Mekong Economic Cooperation Strategy (ACMECS) in reference to the region's three principal rivers.
The meeting adopted a master plan focused on projects to build more connectivity between the group's members. Development partners, including the U.S., China, Japan, South Korea and Australia, then offered in-principle support. A charismatic Thai ambassador for Mekong cooperation has helped lead these efforts.
Yet the push has been slow to yield results. A development fund to finance connectivity projects, announced in 2018, has still not been established. Bangkok now hopes that it might be in place by 2023.
There are signs of improving momentum. In March, Japan said that it would put $1.38 million into the development fund. Though small, this contribution signals some confidence that the fund will be established soon. ACMECS countries have also agreed to set up an interim secretariat.
The slow pace of progress is the result of both political and technical challenges. Most importantly, Vietnam has not been fully supportive of Thailand's ACMECS push.
While Vietnam no longer aspires to hegemony in Indochina, it still adopts an older brother posture toward Cambodia and Laos, frequently convening trilateral meetings and cultivating its political influence. CLMV summits that also bring in Myanmar are a more comfortable format for Hanoi than ACMECS, as it also preserves its preeminence.
At the same time, Cambodia and Laos are skeptical about whether Thailand's regional interest will be sustained and deliver real benefits.
Yet Thailand's push deserves support. As Thai officials point out, of the many competing forums in the subregion, only ACMECS brings together the five mainland Southeast Asian countries.
This means that the group could act as a caucus to develop common positions and greater bargaining power before members meet with much bigger external powers, especially China, which has seized the initiative through its own Lancang-Mekong Cooperation forum.
Caucusing cannot counteract China's influence directly, but as with the Association of Southeast Asian Nations at a wider regional level, it could encourage more solidarity among the lower Mekong countries where their interests align.
ACMECS could also help coordinate efforts across the area's many regional groups, most of which have had no impact on development goals. Aside from China, the U.S., Japan, South Korea and India each hold their own meetings with Mekong states under various formats. Unhelpfully, these forums mostly compete with each other rather than cooperate, sapping the time of Southeast Asian officials and delivering little.
Thailand's partners must encourage Bangkok to treat Hanoi as a real partner because, without Vietnamese buy-in, ACMECS will fail.
Thailand could do this by listening more to Vietnam's suggestions, such as convening ACMECS on the margins of other meetings and focusing on Hanoi's priorities, such as greater east-west connectivity between Vietnam and Laos.
At the same time, partners should encourage Thailand to prioritize ACMECS as a political caucus rather than a builder of physical infrastructure. Its members have disparate priorities and the group has relatively little money at its disposal compared with funders like the Asian Development Bank's Greater Mekong Subregion program.
What would more support for ACMECS look like? Most of the region's major external partners are already signed up as ACMECS development partners.
Like Japan, they could follow this up with financial contributions to the group's development fund. They should also consider channeling other regional cooperative efforts through ACMECS.
For example, policy exchanges and dialogues, which Washington is backing through its Mekong-U.S. Partnership, could be organized under the auspices of ACMECS and badged as such. This would help ensure that cooperation is seen as genuinely collaborative rather than one-sided.
Thailand's interest in drawing the U.S. and other partners into its Mekong agenda presents a rare opportunity to revitalize the two countries' alliance, which has struggled to identify a genuinely shared agenda for cooperation. On most other regional security issues, from the South China Sea to Taiwan, the two are increasingly divergent, mostly because Bangkok does not share Washington's perception that China poses a security threat.
Thailand's Mekong agenda is not about countering China. But the result of a successful ACMECS boosting subregional cooperation and the resilience of Cambodia and Laos would be favorable to U.S. interests in the Indo-Pacific region.