Among the handful of Confederate generals born in the North, Frost led the MVM during the Camp Jackson affair in May 1861 that fanned civil unrest in St. Louis.

[1] He was appointed from New York to the United States Military Academy in nearby West Point and graduated in 1844, ranking 4th in a class of 24.

With the outbreak of the Mexican–American War, he served under Winfield Scott in the Army of Occupation in Mexico and was brevetted for gallantry in action at the Battle of Cerro Gordo.

In the early days of the American Civil War, General Frost supported the secessionist movement endorsed and led by Governor Claiborne Fox Jackson.

In February 1861 Frost enrolled the members of the pro-secession Minutemen para-military organization as Companies in a new Second Regiment, MVM (despite Missouri's "official" policy of neutrality).

He secretly met with Jackson and other secessionist leaders to discuss the possibility of attacking the Federal Arsenal in downtown St. Louis.

At the recommendation of General Frost, Governor Jackson ordered the mustering in of the MVM in St. Louis on May 6, a deployment which would allow an attack on the Arsenal when the Confederate artillery arrived.

Frost's soldiers took possession of the Confederate weapons, and moved them to Camp Jackson, as the MVM encampment was named.

Although he initially denied involvement in any conspiracy when questioned by authorities, Union intelligence later obtained a letter that revealed that Frost was indeed an active participant in Governor Jackson's plotting.

In August 1863, Frost's wife was forced from their home in St. Louis because of the family's ardent Confederate sympathies and had taken the children and moved to Canada for safety and refuge.

General Frost spend much of his time in his later years simultaneously explaining: to Unionists that in May 1861 he had not engaged in pro-Confederate plotting, and to ex-Confederates that he had not deserted from the Confederate States Army in 1863.