Names for the war
Generalissimo Chiang Kai-shek
, Allied Commander-in-Chief in the China theatre from 1942 to 1945
In Allied countries during the war, the "Pacific War" was not usually distinguished from World War II in general, or was known simply as the War against Japan. In the United States, the term Pacific Theater was widely used, although this was a misnomer in relation to the British campaign in Burma, the war in China and other activities within the Southeast Asian Theater.
Japan used the name Greater East Asia War (大東亜戦争 Dai Tō-A Sensō), as chosen by a cabinet decision on 10 December 1941, to refer to both the war with the Western Allies and the ongoing war in China. This name was released to the public on 12 December, with an explanation that it involved Asian nations achieving their independence from the Western powers through armed forces of the Greater East Asia Co-Prosperity Sphere. Japanese officials integrated what they called the Japan–China Incident (日支事変 Nisshi Jihen) into the Greater East Asia War.
During the Allied military occupation of Japan (1945–52), these Japanese terms were prohibited in official documents, although their informal usage continued, and the war became officially known as the Pacific War (太平洋戦争 Taiheiyō Sensō). In Japan, the Fifteen Years' War (十五年戦争 Jūgonen Sensō) is also used, referring to the period from the Mukden Incident of 1931 through 1945.
Political map of the Asia-Pacific region, 1939
The Axis states which assisted Japan included the authoritarian government of Thailand in World War II, which quickly formed a temporary alliance with the Japanese in 1941, as the Japanese forces were already invading the peninsula of southern Thailand. The Phayap Army sent troops to invade and occupy northeastern Burma, which was former Thai territory that had been annexed by Britain much earlier. Also involved were the Japanese puppet states of Manchukuo and Mengjiang (consisting of most of Manchuria and parts of Inner Mongolia respectively), and the collaborationist Wang Jingwei regime (which controlled the coastal regions of China). In preparation for the war against the United States, which would be decided at sea and in the air, Japan increased its naval budget as well as putting large formations of the Army and its attached air force under navy command. While formerly the IJA consumed the lion's share of the state's military budget due to the secondary role of the IJN in Japan's campaign against China (with a 73/27 split in 1940), from 1942 to 1945 there would instead be a roughly 60/40 split in funds between the army and the navy.
The official policy of the US government is that Thailand was not an ally of the Axis, and that the United States was not at war with Thailand. The policy of the US government ever since 1945 has been to treat Thailand not as a former enemy, but rather as a country which had been forced into certain actions by Japanese blackmail, before being occupied by Japanese troops. Thailand has been treated by the United States in the same way as such other Axis-occupied countries as Belgium, Czechoslovakia, Denmark, Greece, Norway, Poland, and the Netherlands.
Japan conscripted many soldiers from its colonies of Korea and Formosa (Taiwan). To a small extent, some Vichy French, Indian National Army, and Burmese National Army forces were active in the area of the Pacific War. Collaborationist units from Hong Kong (reformed ex-colonial police), Philippines, Dutch East Indies (the PETA) and Dutch Guinea, British Malaya and British Borneo, Inner Mongolia and former French Indochina (after the overthrow of Vichy French regime) as well as Timorese militia also assisted Japanese war efforts.
Germany and Italy both had limited involvement in the Pacific War. The German and the Italian navies operated submarines and raiding ships in the Indian and Pacific Oceans. The Italians had access to "concession territory" naval bases in China, while the Germans did not. After Japan's attack on Pearl Harbor and the subsequent declarations of war, both navies had access to Japanese naval facilities.
The major Allied participants were the United States, China, the United Kingdom (including the armed forces of British India, the Fiji Islands, Samoa, etc.), Australia, the Commonwealth of the Philippines, the Netherlands (as the possessor of the Dutch East Indies and the western part of New Guinea), New Zealand, and Canada, all of whom were members of the Pacific War Council. Mexico, Free France and many other countries also took part, especially forces from other British colonies.
The Soviet Union fought two short, undeclared border conflicts with Japan in 1938 and 1939, then remained neutral until August 1945, when it joined the Allies and invaded the territory of Manchukuo, China, Inner Mongolia, the Japanese protectorate of Korea and Japanese-claimed islands such as Sakhalin.
The Pacific War Council as photographed on 12 October 1942. Pictured are representatives from the United States (seated), China, the United Kingdom, Australia, Canada, the Netherlands, New Zealand, and the Philippine Commonwealth
Between 1942 and 1945, there were four main areas of conflict in the Pacific War: China, the Central Pacific, South-East Asia and the South West Pacific. US sources refer to two theaters within the Pacific War: the Pacific theater and the China Burma India Theater (CBI). However these were not operational commands.
In the Pacific, the Allies divided operational control of their forces between two supreme commands, known as Pacific Ocean Areas and Southwest Pacific Area. In 1945, for a brief period just before the Japanese surrender, the Soviet Union and its Mongolian ally engaged Japanese forces in Manchuria and northeast China.