By 1941, the war was entering its darkest days. Germany had invaded the Soviet Union, and the Japanese attacks on Pearl Harbor and several British overseas colonies, had ignited the Pacific War. China was embroiled in a desperate struggle to resist the Japanese invasion. Japanese forces were bombing China’s major cities day and night; at the same time, they were conducting operations,aimed at encircling the rear areas. The campaign to cut China off, had left only one line of communication open with the West – the Yunnan-Burma Road in China’s southwest. Meanwhile Britain, deeply involved in the European theatre, had made its strategic priority in the Far East, the protection of India. At the end of 1941, China and Britain established a military alliance,and on February the 25th, 1942, a one-hundred-thousand-strong Chinese Expeditionary Force began to enter Burma.