The BIA reached the Burmese border in January 1942. Their force grew as it advanced through Burma, taking as many recruits with it as it could along the way. By the time the BIA reached Rangoon on 18 March 1942 it was 10,000 men strong, and by May 1942 it had 23,000 soldiers. The BIA left most of the fighting to the Japanese Army but occupied the areas behind Japanese lines after the British had retreated. The arrival of BIA units in many areas of Burma was followed by escalating communal violence, especially against Karen people, which lasted for several weeks until the Japanese Army was able to intervene. Throughout the war the Burmese Independence Army would be responsible for numerous massacres and "reprisal" attacks on civilian areas perceived to be more loyal to the British than themselves, especially in the Irrawaddy Delta, Tenessarrim Division, and in the Karen Hills, and especially against non-Buddhist, non-Bamar communities.