On July 3, 1861,
President Abraham Lincoln appointed
Major General John C. Fremont to command the Department of the West, headquartered at St. Louis. Already chief quartermaster when Fremont took command of the department, McKinstry was appointed a major and assistant quartermaster in the U.S. Army on August 3, 1861, and continued his assignment in the Department of the West. McKinstry's actions in restricting movements into and out of the city, instituting a 9:00 p.m. curfew and censoring the press made him, and Fremont, unpopular with many of the city's residents. Historian
Bruce Catton cites McKinstry as performing a great service to the
Union cause by introducing Brigadier General
Ulysses S. Grant to Fremont. Fremont had considered appointing Brigadier General
John Pope to the important post at
Cairo, Illinois but after his meeting with Grant, Fremont decided to appoint Grant instead. McKinstry was an old West Point and regular army friend of Grant and assured Fremont that rumors of Grant's drinking habits were exaggerated and he would be stable if given a responsible command. Fremont had kept Grant waiting for hours after having summoned him to his headquarters in St. Louis. When McKinstry passed by and asked Grant about his wait, Grant told him the circumstances. McKinstry immediately got Fremont's attention and told him that he had observed Grant's gallantry in Mexico and that he was a reliable man for the job. In response to growing pressure from influential persons such as Missouri
Congressman Frank Blair, who was interested in obtaining more contracts for his friends but was unsuccessful in obtaining them from McKinstry, Fremont obtained McKinstry's removal as quartermaster from
Quartermaster General Montgomery C. Meigs but kept him as provost marshal and then assigned him to a division command from September 2, 1861, to November 7, 1861, McKinstry was appointed a brigadier general of volunteers on September 2, 1861, but the appointment expired without confirmation by the United States Senate on July 17, 1862. Fremont assigned McKinstry to command Division 5 of the Department of the West between September 24, 1861, and October 24, 1861, as Fremont's army of five divisions, about 30,000 men, moved out toward
Springfield, Missouri in an effort to capture the strategically located town from
Confederate Missouri State Guard forces under
Major General Sterling Price. Zagonyi's small Union force briefly occupied the town but withdrew because they had lost many of their horses during the fight and the Confederates would have outnumbered them if they had counter-attacked. On October 27, 1861, Union troops returned to occupy the town in force. During his time under suspension and arrest, McKinstry wrote
Vindication of Brig. Gen. J. McKinstry, Formerly Quarter-Master, Western Department. Based on an examination of this document, the court-martial record and other circumstances, historian G. E. Rule is more sympathetic to McKinstry's actions and circumstances than many other historians.
Allan Nevins also cites Frank Blair's interference with Fremont and efforts to get McKinstry to give contracts to Blair's shady friends, without placing blame on McKinstry for supply problems. Warner noted that McKinstry was one of only three Union Army generals to be cashiered during the American Civil War. Warner and Longacre state that McKinstry's sentence was the only one of its kind given to a general officer during the war. == Later life and death ==