In Burma, the British, under intense pressure, made a fighting retreat from Rangoon to the Indo-Burmese border. This cut the Burma Road, which was the western Allies' supply line to the Chinese Nationalists. In March 1942, the Chinese Expeditionary Force started to attack Japanese forces in northern Burma. On 16 April, 7,000 British soldiers were encircled by the Japanese 33rd Division during the Battle of Yenangyaung and rescued by the Chinese 38th Division, led by Sun Li-jen. Cooperation between the Chinese Nationalists and the Communists had waned from its zenith at the Battle of Wuhan, and the relationship between the two had gone sour as both attempted to expand their areas of operation in occupied territories. The Japanese exploited this lack of unity to press ahead in their offensives.