Question: In what US city is the Sixth Army headquartered?

Context paragraphs:
United States Army Training and Doctrine Command: Established 1 July 1973, the United States Army Training and Doctrine Command (TRADOC) is a command of the United States Army headquartered at Fort Eustis, Virginia.  It is charged with overseeing training of Army forces and the development of operational doctrine.  TRADOC operates 37 schools and centers at 27 different locations.  TRADOC schools conduct 1,304 courses and 108 language courses.  The 1,304 courses include 516,000 seats (resident, on-site and distributed learning) for 443,231 soldiers; 36,145 other-service personnel; 8,314 international soldiers; and 28,310 civilians.

Canadian Army Doctrine and Training Centre: The Canadian Army Doctrine and Training Centre (CADTC) (French: "Centre de la doctrine et de l'instruction de l'Armée canadienne)," formerly the Land Force Doctrine and Training System (LFDTS), is a formation of the Canadian Army headquartered at McNaughton Barracks, CFB Kingston, Ontario.  CADTC is the organization that is responsible for delivering army training and developing army doctrine.  Approximately 3,200 officers and soldiers are assigned to CADTC.  The organization was renamed on 18 July 2013 as part of the reorganization of the Canadian Army.

I Corps (Pakistan): The I Corps, also known as I Strike Corps, of the Pakistan Army headquartered in Mangla, Azad Kashimir Territory of Pakistan.  Known as I Strike Corps, it is one of two strike corps within its ten manoeuvre Army corps.  The I Strike Corps is one of the oldest and major formations of Pakistan Army, and a major component of Northern Military Command of Pakistan Defence Forces.

Battle of Guillemont: The Battle of Guillemont (3–6 September 1916) was an attack by the Fourth Army on the village of Guillemont.  The village is on the D 20 running east to Combles and the D 64 south-west to Montauban.  Longueval and Delville Wood lie to the north-west and Ginchy to the north-east.  The village was on the right flank of the British sector, near the boundary with the French Sixth Army.  The Fourth Army had advanced close to Guillemont during the Battle of Bazentin Ridge (14–17 July) and the capture of the village was the culmination of British attacks which began on 22/23 July.  The attacks were intended to advance the right flank of the Fourth Army and eliminate a salient further north at Delville Wood.  German defences ringed the wood and had observation over the French Sixth Army area to the south, towards the Somme river.

166th Aviation Brigade (United States): The 166th Aviation Brigade was an aviation training brigade of the United States Army headquartered at Fort Hood, Texas.  It was a subordinate unit of First Army - Division West.  An "AC/RC" (Active Component / Reserve Component) formation, the 166th Aviation Brigade was the sole organization responsible for the post-mobilization training of United States Army Reserve & National Guard aviation units.  The unit was formerly designated as 3rd Brigade, 75th Division.

Battle of Kalach: The Battle of Kalach took place between the German Sixth Army and elements of the Soviet Stalingrad Front between July 25 and August 11, 1942.  The Soviets deployed the 62nd and 64th Armies in a Don River bridgehead west of Kalach with the intent of impeding the German advance on Stalingrad.  In the initial period of the battle, the Germans attacked and managed to surround part of the 62nd Army.  In reaction, the Soviets counter-attacked and temporarily forced the Germans onto the defense.  Following resupply of German forces, the roles again reversed and the Germans attacked into the flanks of the Soviet bridgehead, successfully collapsing it.  The German victory positioned the Sixth Army to cross the Don River and advance on Stalingrad, which became the site of one of the most decisive battles of World War II.

Fort Sam Houston: Fort Sam Houston is a U.S. Army post in San Antonio, Texas.

16th Military Police Brigade (United States): The 16th Military Police Brigade is a Military Police brigade of the United States Army headquartered at Fort Bragg, North Carolina.  This military police unit was the only airborne-qualified military police brigade in the United States Army.  It provides law enforcement and police duties to the Fort Bragg area, and for the XVIII Airborne Corps when deployed.  As an airborne unit, it was authorized a beret flash and parachute wing trimming, and the shoulder sleeve insignia was authorized to be worn with an airborne tab.  According to U.S. Army's Institute of Heraldry, the shoulder sleeve insignia "was amended to delete the airborne tab effective 16 October 2008" when jump status was terminated.

109th Military Intelligence Battalion: The 109th Military Intelligence Battalion is a multidiscipline Military Intelligence battalion of the United States Army headquartered at Joint Base Lewis-McChord, Washington.  A Regular Army Military Intelligence Battalion, it is one of the subordinate battalions of the 201st Expeditionary Military Intelligence Brigade, which is part of the US Army's 7th Infantry Division and I Corps.

Sixth United States Army: Sixth Army is a field army of the United States Army.  The Army service component command of United States Southern Command, its area of responsibility includes 31 countries and 15 areas of special sovereignty in Central and South America and the Caribbean.  It is headquartered at Fort Sam Houston.

Supporting paragraphs: Sixth United States Army Fort Sam Houston
Answer: San Antonio, Texas.