This caused a rapid deterioration of relations with Britain and the United States. In April 1941 the United States cut off petroleum supplies to Thailand. Thailand's brief period of glory came to an end on 8 December 1941 when Japan invaded the country along its southeastern coastline and from Cambodia. After initially resisting, the Phibun regime gave in and allowed the Japanese to pass through the country to attack Burma and invade Malaya. Convinced by the Allied defeats of early 1942 that Japan was winning the war, Phibun decided to form a military alliance with Imperial Japan.