When the Japanese invaded Thailand on 8 December 1941, (because of the international date line this occurred an hour and a half before the attack on Pearl Harbor), Phibun was reluctantly forced to order a general ceasefire after just one day of resistance and allow the Japanese armies to use the country as a base for their invasions of the British colonies of Burma and Malaya. Hesitancy, however, gave way to enthusiasm after the Japanese rolled through the Malayan Campaign in a "Bicycle Blitzkrieg" with surprisingly little resistance. On 21 December Phibun signed a military alliance with Japan. The following month, on 25 January 1942, Phibun declared war on Britain and the United States. South Africa and New Zealand declared war on Thailand on the same day. Australia followed soon after. Phibun purged all who opposed the Japanese alliance from his government. Pridi Banomyong was appointed acting regent for the absent King Ananda Mahidol, while Direk Jayanama, the prominent foreign minister who had advocated continued resistance against the Japanese, was later sent to Tokyo as an ambassador. The United States considered Thailand to be a puppet state of Japan and refused to declare war on it. When the Allies were victorious, the United States blocked British efforts to impose a punitive peace.