In 1940 France was occupied by Germany, and Phibun immediately set out to avenge Siam’s humiliations by France in 1893 and 1904. By agreement with Japan, Thai troops occupied Lao territory west of the Mekong, and also western Cambodia. This caused a rapid deterioration of relations with the United States and Britain. In April 1941 the U.S. cut off oil supplies to Thailand. The democratic forces were anti-Japanese, and in August the National Assembly voted to resist Japanese pressure by a mass popular mobilisation. But Phibun controlled the army, and when World War II broke out in the Pacific in December, after a brief show of resistance at the battle of Prachuab Khirikhan, he allied Thailand with Japan, allowing Japanese troops to pass through the country to attack the British in Malaya and Burma.