Question: What major American war did the Union corps commander born in 1827 fight in?

Context paragraphs:
Fort Slocum: Fort Slocum, New York was a US military post which occupied Davids' Island in the western end of Long Island Sound in the city of New Rochelle, New York from 1867 to 1965.  The fort was named for Major General Henry W. Slocum, a Union corps commander in the American Civil War.

Oliver Otis Howard: Oliver Otis Howard (November 8, 1830 – October 26, 1909) was a career United States Army officer and a Union general in the American Civil War.  As a brigade commander in the Army of the Potomac, Howard lost his right arm while leading his men against Confederate forces at the Battle of Fair Oaks/Seven Pines in June 1862, an action which later earned him the Medal of Honor.  As a corps commander, he suffered two humiliating defeats at Chancellorsville and Gettysburg in May and July 1863, but recovered from the setbacks as a successful corps and later army commander in the Western Theater.

12th West Virginia Volunteer Infantry Regiment: The 12th West Virginia Volunteer Infantry Regiment was an infantry regiment that served in the Union Army during the American Civil War.  The regiment was particularly distinguished for its successful attack on Fort Gregg during the 1864 to 1865 Siege of Petersburg, receiving a golden eagle for its flagstaff as a token of appreciation from corps commander John Gibbon.

Georgy Kharaborkin: Georgy Filimonovich Kharaborkin (Russian: Георгий Филимонович Хараборкин ; 23 November 1905 – 6 July 1941) was a Red Army captain and a Hero of the Soviet Union.  Kharaborkin was awarded the title for his leadership of a tank company in the Winter War, during which his company broke through the Mannerheim Line.  He became a battalion commander in the 7th Mechanized Corps' 14th Tank Division after the end of the war.  After the German invasion of the Soviet Union in June 1941, Kharaborkin's unit was sent into combat, in an action known as the Lepel counterattack.  Before the counterattack began, his corps commander sent Kharaborkin and a dozen heavy tanks on a reconnaissance in force to find fords across a river.  The detachment was destroyed on the morning of 6 July when it ran into a German minefield covered by anti-tank guns and artillery, and Kharaborkin was killed.

John Gibbon: John Gibbon (April 20, 1827 – February 6, 1896) was a career United States Army officer who fought in the American Civil War and the Indian Wars.

Henry Warner Slocum: Henry Warner Slocum, Sr. (September 24, 1827 – April 14, 1894), was a Union general during the American Civil War and later served in the United States House of Representatives from New York.  During the war, he was one of the youngest major generals in the Army and fought numerous major battles in the Eastern Theater and in Georgia and the Carolinas.  While commanding a regiment, a brigade, a division, and a corps in the Army of the Potomac, he saw action at Bull Run, the Peninsula, South Mountain, Antietam, Chancellorsville, and Harpers’ Ferry.  At Gettysburg, he was the senior Union General in the Field.  During the battle, he held the Union right from Culp’s Hill to across the Baltimore Pike.  His successful defense of Culp’s Hill was crucial to the Union victory at Gettysburg.  After the fall of Vicksburg, Slocum was appointed military commander of the district.  Slocum participated in the Atlanta campaign and was the first commander to enter the city on September 2, 1864.  He then served as occupation commander of Atlanta.  Slocum was appointed the commander of the left wing of Sherman’s march through Georgia and the Carolinas, commanding the XIV and XX Corps, comprising the Army of Georgia.  During this campaign, he captured the capitol of Georgia, Milledgeville, and the seaport of Savannah.  In the Carolinas campaign, Slocum’s army saw victories in the battles of Averasborough and Bentonville, North Carolina.  The March to the Sea and the Carolinas campaign were crucial to the overall Union victory in the Civil War.  After the surrender of Confederate forces, Slocum was given command of the Department of Mississippi.  Slocum declined an appointment in the postwar Army.  He was a successful political leader, businessman and railroad developer.

II Corps (Pakistan): The II Corps, known as II Strike Corps or Army Reserve South, is army corps of Pakistan Army stationed in Multan, Punjab Province of Pakistan.  The II Strike Corps is one of Pakistan's four heavy armoured corps.  Also known as Army Reserve South, the corps is currently active in Pakistan's theatre in War on Terror where its administrative divisions and brigades led numerous operations in the Federally Administered Tribal Areas of Pakistan.  The Corps is currently commanded by 3-star general Lieutenant-General Sarfraz Sattar as Corps Commander.  The Corps longest-serving Commander was then Lieutenant-General Rahimuddin Khan.

James Longstreet: James Longstreet (January 8, 1821January 2, 1904) was one of the foremost Confederate generals of the American Civil War and the principal subordinate to General Robert E. Lee, who called him his "Old War Horse."  He served under Lee as a corps commander for many of the famous battles fought by the Army of Northern Virginia in the Eastern Theater, but also with Gen. Braxton Bragg in the Army of Tennessee in the Western Theater.  Biographer and historian Jeffry D. Wert wrote that Longstreet, "was the finest corps commander in the Army of Northern Virginia; in fact, he was arguably the best corps commander in the conflict on either side."

XXX Corps (Pakistan): The XXX Corps (30 Corps), known as Triple X Corps, is an active military administrative corps of Pakistan Army currently assigned in Gujranwala, Punjab Province.  The Corps is a major and integral part of Eastern Military Command of Pakistan Defence Forces, along with PAF's Eastern Air Command and Navy's Eastern Naval Command.  It is currently commanded by Lieutenant-General Ikram Ul Haq, who is designated as Corps Commander of this holding corps.

Roman Ivanovich Panin: Roman Ivanovich Panin (Russian: Роман Иванович Панин ; 28 September 1897 – 1 June 1949) was a Soviet major general from during World War II.  An Imperial Russian Army junior officer in World War I, he joined the Red Army in 1919.  Panin fought in the Russian Civil War and continued to serve after the end of the Russian Civil War.  He was an advisor to the National Revolutionary Army between 1938 and 1939.  Later he participated in the Soviet-Finnish war as a corps commander, and during World War II as the commander of the 14th Army, commanding the defense of Murmansk during Operation Silver Fox.  Panin became commander of the 2nd Reserve Army in May 1942 and two months later became a lecturer at the Frunze Military Academy.  In February 1943 he became Volkhov Front chief of combat training and in September led the 7th Rifle Corps.  After participating in the Leningrad–Novgorod Offensive, Panin briefly led the 99th Rifle Corps.  In July 1944, Panin became deputy commander of the 5th Army.  Hospitalized in February 1945 during the East Prussian Offensive, Panin did not see further action.  After recovering he became an instructor at the Frunze Military Academy and retired in 1949.  He died shortly afterwards.

Supporting paragraphs: 12th West Virginia Volunteer Infantry Regiment John Gibbon
Answer: American Civil War