In recent years, relations with Southeast Asia have emerged as an important pillar of US engagement with the Indo-Pacific region. The Association of Southeast Asian Nations (ASEAN) is central to US foreign policy in the region, with a growing focus on the five countries bound together by the Mekong River—Cambodia, Lao PDR, Myanmar, Thailand, and Vietnam. In recent years, relations with Southeast Asia have emerged as an important pillar of US engagement with the Indo-Pacific region. The Association of Southeast Asian Nations (ASEAN) is central to US foreign policy in the region, with a growing focus on the five countries bound together by the Mekong River—Cambodia, Lao PDR, Myanmar, Thailand, and Vietnam.