In the wake of the Russia—Ukraine war that began in February 2022, Russia faced an barrage of tough international sanctions. Meanwhile, the United States and Europe attempted to pressure China to assume a more responsible position in the international armed conflict.

The launch of the Lancang-Mekong Cooperation (LMC) opened a fresh chapter in international politics in the Mekong region, by marking China’s official entry into the continental Southeast Asian arena. However, little is known about the LMC’s evolution. By extensively relying on the recently opened Archives in Bangkok, this article illuminates facts and narrates the LMC’s formation, with special emphasis on the Chinese perspective.