After Paris fell, Japanese forces invaded Indochina
Thailand (Jan 1941) sent troops across the border of Thailand & Indochina to seize parts of French Cambodia
The Japanese acted as a broker: ceded two chunks of territories to Thailand.
Phibun urged the cabinet to comply to the Japanese’s request for the troop passage through Thailand to attack British in Malaya & Burma
8 Dec 1941: the Japanese troops landed and was granted a safe passage Jan. 1942: Thailand formally declared war on Britain & the U.S.A.
With the “Pan-Thai” in mind, Phibun told the Cabinet: “We shouldn’t let them[Japan] build Asia alone …”