Editing Corps area (section)

== National Defense Act of 1920 and establishment of corps area-level organizations ==
Authorized by the National Defense Act of 1920, which amended the [[National Defense Act of 1916]], nine multi-state sized "corps areas" were established on 20 August 1920 by the U.S. Army Chief of Staff through War Department General Order Number 50. The corps areas were formed for administration, training, and tactical control of the army, replacing the six geographical (or territorial) military departments into which the continental United States had been divided since 1917 and with little variation since the Civil War. Three overseas commands: the [[Hawaiian Department]], [[United States Southern Command|Panama Canal Department]], and the [[Philippine Department]] continued to be identified as departments.<ref>{{Citation
  |title =The Brooklyn Daily Eagle Almanac
  |publisher=Brooklyn Daily Eagle
  |year=1921
  |location =Brooklyn, New York
  |pages =295
  |oclc = 1586159}}</ref>

The 1920 act was a realization that the mobilization of a citizen army could no longer meet the defense needs of the United States and for the first time placed an emphasis on peacetime preparedness. Yet with its passage, Congress never fully funded the program. But Congress did recognize the value of a professional officer education program by enhancing existing general service schools such as the [[Command and General Staff College|Command and General Staff School]] at [[Fort Leavenworth]], Kansas, and the [[United States Army War College|Army War College]] at [[Fort Lesley J. McNair|Washington Barracks]], District of Columbia. The act authorized the establishing new schools to meet modern military educational needs, such as the [[Army Industrial College]] in 1924. Thirty-one additional special service schools were established or improved to provide training to the various branches of the Army.

The act established the [[Division (military)|division]] as a basic Army unit, replacing the pre-World War I notion of the regiment in war planning. Tactically and administratively, each corps area commander was the senior army officer for his geographical area, typically functioning as a commanding general of an existing Regular Army corps or division in their area. During times of [[Civil disorder|civil unrest]], [[Strike action|labor strikes]], or [[natural disaster]]s, corps area commanders provided Army resources needed to address the emergency.

Each corps area was allocated two [[corps (military)|"type" corps]] (with a standard table of organization) and six infantry divisions. The corps were numbered in accord with their corps area designation, i.e. I and XI Corps in the First Corps Area. The lower numbered corps (I through IX) consisted of one Regular Army and two [[National Guard of the United States|National Guard]] divisions among the various states of the corps area. The higher numbered corps (XI through XIX) each consisted of three divisions, also assigned by state boundaries, of the newly established (but rarely funded) [[United States Army Reserve|Organized Reserve]]. By 1925, in the face of steady [[Coolidge Administration]] and congressional budget cutting, the United States Army only had three active regular divisions nationwide; the remainder of its divisions, both regular and reserve components, only existed on paper.

The amended National Defense Act also grouped three corps areas into an "army level" mobilization organization whose boundaries were also identical for the two "type" [[field army|armies]] located within them. For example, First, Second, and Third Corps Areas, and the First and Fourth (Field) Armies, comprised the First "Army Area". The 1921 mobilization planning that created the six field army headquarters did not envision a need for active field army-level commands in peacetime and thus the headquarters were constituted in the Organized Reserve rather than the Regular Army.

Until fully activated with its own headquarters staff, an army area was typically jointly staffed, headquartered, and commanded by the most senior corps commander in that area. Between 1927 and 1933 all six field army headquarters were deactivated as the Army wrestled with structure, mobilization, and manpower issues.