To isolate the US forces stationed in the Philippines and to reduce US naval power, the Imperial General Headquarters ordered an attack on the US naval base at Pearl Harbor, Hawaii, on 7 December 1941. They also invaded Malaya and Hong Kong. Initially achieving a series of victories, by 1943 the Japanese forces were driven back towards the home islands. The Pacific War lasted until the atomic bombings of Hiroshima and Nagasaki in 1945. The Soviets formally declared war in August 1945 and engaged Japanese forces in Manchuria and northeast China.