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|Chain of command|
|army group||400,000–1,000,000||field marshal|
|army region||1,000,000–3,000,000||field marshal|
An army group is a military organization consisting of several field armies, which is self-sufficient for indefinite periods. It is usually responsible for a particular geographic area. An army group is the largest field organization handled by a single commander—usually a full General or Field Marshal—and it generally includes between 400,000 and 1,000,000 soldiers.
Army groups may be multi-national formations. For example, during World War II, the Southern Group of Armies (also known as the U.S. 6th Army Group) comprised the U.S. Seventh Army and the French First Army; the 21st Army Group comprised the British Second Army, the Canadian First Army and the US Ninth Army.
In U.S. Army usage, the number of an army group is expressed in Arabic numerals (e.g., "12th Army Group"), while the number of an army is spelled out (e.g., "Third Army").
World War II 
A Chinese "army group" was usually equivalent in numbers only to a field army in the terminology of other countries. On 16 May 1940, Zhang Zizhong, commander of the 33rd Army Group was killed in action in Hubei province. He was the highest ranking Chinese officer to be killed in the war.
The German Army was organized into army groups (Heeresgruppen). (See List of German Army Groups in WWII.) Some of these army groups were multinational, containing armies from several Axis countries. For example Army Group Africa contained both German and Italian corps.
During World War II there were six General Armies:
- Kantōgun (often known as the "Kwantung Army") originated as the division-level garrison of a Japanese colony in northeast China, in 1908; it remained in northern China until the end of World War II. The strength of the Kantōgun peaked at 700,000 personnel in 1941. It faced and was destroyed by Soviet forces in 1945.
- Shina Hakengun, the "China Expeditionary Army", was formed in Nanjing, in September 1939, to control operations in central China. At the end of World War II, it consisted of 620,000 personnel in 25 infantry and one armored divisions.
- Nanpo Gun was the "Southern Army", also known as the "Southern Expeditionary Army". By November 1941, war with the western Allies appeared likely and Nanpo Gun was formed in Saigon, French Indochina, to control IJA operations in southern China, South Asia, South East Asia, and the South Pacific.
In April 1945, the Boei So-Shireibu (translated as "General Defense Command" or "Home Defense General Headquarters" and similar names) was split into three General Armies:
- Dai-Ichi So-Gun ("1st General Army", headquartered in Tokyo)
- Dai-Ni So-Gun ("2nd General Army", headquartered in Hiroshima)
- Koku So-Gun ("Air General Army", headquartered in Tokyo)
By August 1945, these comprised two million personnel in 55 divisions and numerous smaller independent units. After the surrender of Japan, the IJA was dissolved, except for the Dai-Ichi So-Gun, which existed until 30 November 1945 as the 1st Demobilization Headquarters.
Soviet Union 
The Soviet Army was organized into Fronts (фронт pl. фронты) which were often as large as an army group. (See List of Soviet fronts in World War II.) Some of the Fronts contained Allied formations raised in exile. For example, the Polish First Army was part of the 1st Belorussian Front.
Western Allies 
North West Europe 
In April 1944, the previously informal Western Allied collaboration in the North West Europe was strengthened by the establishment in London of a formal planning headquarters called Chief of Staff Supreme Allied Command (COSSAC). In February 1944, this headquarters was replaced by the final interallied headquarters for the Theater—Supreme Headquarters Allied Expeditionary Forces (SHAEF). SHAEF was the operational command, headed by General Dwight D. Eisenhower, that planned the invasion and issued operational commands once the invasion took place.
Eisenhower also became (in January 1944) the commanding general of the European Theater of Operations United States Army (ETOUSA) that was responsible for the administration of American forces in the theater (dealing with matters such as pay and recreation). The staff organizations of SHAEF and ETOUSA were distinct. As a rule, each headquarters had its own staff sections manned by separate personnel. The staff organization in SHAEF was headed by the Chief of Staff and had as an important officer the Secretary of the General Staff. The G-2 and G-3 divisions of SHAEF, which comprise a portion of this accession, functioned according to the United States War Department General Staff pattern.
SHAEF had operational control over three inter-Allied ground commands known as Army Groups. The initial two were the 21st Army Group and the 12th Army Group (originally the U.S. 1st Army Group or FUSAG), and in September 1944, operational command of the Sixth Army Group (which had landed in the south of France during Operation Dragoon) passed from Allied Force Headquarters (AFHQ) to SHAEF. As part of the pre-invasion deception plan called Operation Quicksilver, the original FUSAG was renamed 12th Army Group, and "FUSAG" continued as a notional army group threatening to invade France across the Straits of Dover.
South East Asia 
South East Asia Command (SEAC) in the South-East Asian theater had operational command of the British 11th Army Group that was later reorganised and redesignated Allied Land Forces South East Asia (ALFSEA). Like most other Western Allied army groups, ALFSEA co-ordinated a mixture of Allied forces from several nations.
NATO 'Army Groups' 
During the Cold War, NATO land forces in what was designated the Central Region (most of the Federal Republic of Germany) would have been commanded in wartime by two 'Army Groups'. Under Allied Forces Central Europe and alongside air force elements, the two Army Groups would have been responsible for the defence of Germany against any Soviet/Warsaw Pact invasion. These two Principal Subordinate Commanders (PSCs) had only limited peacetime authorities, and issues such as training, doctrine, logistics, and rules of engagement (ROE) were largely a national, rather than Alliance, responsibility.
The two formations were the 'Northern Army Group' (NORTHAG) and the 'Central Army Group' (CENTAG). By World War II and previous standards these two formations were only armies, as they contained four corps each. NORTHAG consisted, from north to south, of I Netherlands Corps (I (NE) Corps), I German Corps (I (GE) Corps), I (BR) Corps, and I Belgian Corps (I (BE) Corps). Its commander was the British commander of the British Army of the Rhine (BAOR). CENTAG consisted, from north to south, of III (GE) Corps, V US Corps, VII (US) Corps, and II (GE) Corps in the extreme south of the Federal Republic of Germany. The commander of the United States Army Europe commanded CENTAG.
In November 1991, the NATO heads of state and government adopted the "New Strategic Concept" at the NATO Summit in Rome. This new conceptual orientation led, among other things, to fundamental changes both in the force and integrated command structure. Structural changes began in June 1993, when HQ Central Army Group (CENTAG) at Heidelberg and Northern Army Group (NORTHAG) at Mönchengladbach, GE were deactivated and replaced by Headquarters Allied Land Forces Central Europe (LANDCENT), which was activated at Heidelberg on 1 July 1993.