In the summer of 1864 guerrilla warfare was causing chaos in North Missouri and Union General William S. Rosecrans wrote to the Secretary of War, Edwin M. Stanton,
“I regret to say matters in north Missouri are very disturbed and threatening. Union men are fleeing from the river counties and central part of the State. The malcontented spirits, and uprising of bushwhackers, with threats from the conspirators, are ominous of evil… Informing you of these things, I suggest that we will be obligated to have some other troops here, and if nothing better can be done, the state of things would be best met from our own resources, by authority from me to accept the services of, say, 5,000 volunteers for the defense of the state, in companies, to be armed, equipped, and paid by the Government.”
From the Official Records of the War of the Rebellion Series I Vol XLI Part 2, page 234.