On 28 December 1942, a group of young Burmese independence activists, called the Thirty Comrades, who had received military training by the Japanese, founded the Burma Independence Army  in Bangkok. The army led by Aung San fought in the Burma Campaign on the side of the Imperial Japanese Army. It saw a significant engagement at Shwedaung near Prome against the British in March 1942. Thousands of young men joined its ranks—reliable estimates range from 15,000 to 23,000. The great majority of the recruits were Burman, with little ethnic minority representation. Many of the fresh recruits lacked discipline. At Myaungmya in the Irrawaddy delta, an ethnic war broke out between Burman BIA men and Karens, with both sides responsible for massacres. The BIA was soon replaced with the Burma Defense Army, founded on 26 August 1942 with three thousand BIA veterans. The army became Burma National Army  with Ne Win as its commander on 1 August 1943 when Burma received nominal independence. In late 1944, it had a strength of approximately 15,000. Disillusioned by the Japanese occupation, the BNA realigned with the allied forces on 27 March 1945.
Question: who did the Imperial Japanese Army fight against?
Answer: the British