Thailand and Vichy France sign Tokyo Convention under Japanese mediation

Multiple reputable sources, including Wikipedia articles on the Franco-Thai War and Battle of Ko Chang, consistently confirm that on 9 May 1941, under Japanese mediation, Thailand and Vichy France signed the Tokyo Convention, which awarded Thailand the western Cambodian provinces of Battambang, Siem Reap, and Sisophon along with parts of Laos. The sources agree on the date, the mediator, and the territorial cessions, with no credible contradiction found. The Franco-Thai War article explicitly states the treaty was signed in Tokyo on 9 May 1941, and the Battle of Ko Chang article notes Japan's diplomatic intervention led to a ceasefire and peace negotiations.