Although Australia had been at war with Germany since 1939, the impact of war increased dramatically after the Japanese entered it in 1941. The Japanese forces swept south through Malaya, the Netherlands East Indies and had reached New Guinea by January, 1942. Northern Australia became a major staging point. General Headquarters South West Pacific Area, under the command of US General Douglas MacArthur, was also moved to Brisbane in July 1942. An unprecedented military build-up followed. The concentration of US troops alone was heaviest in south-east Queensland, reaching a peak of 75,500 in December 1943. Camps, airfields, construction and recreational facilities specifically for the US Army were erected in Brisbane during the war.