The Missouri bushwhackers are a ruthless gang of Southern partisans who stage regular raids on Union forces. They have a fearsome reputation for violence, which they carry out indiscriminately against not just soldiers, but innocent civilians too. The latter include Jeff's family, whose farm in Kansas is attacked by by a gang of bushwhackers from across the border. The irony here is that Jeff's named after Jefferson Davis, President of the Confederacy, under whom his father served during the Mexican War. But the Missouri bushwhackers don't know about any of this; nor would it make much difference if they did. All they care about is plunder and destruction.
After the family farm is attacked, Jeff signs up to join the Union army. He sees this as his big chance to hit back at the bushwhackers and the Confederacy they support. As with many young men of his age, he has dreams of war as a great adventure, full of glory and heroism. However, it isn't very long before Jeff's thoroughly disillusioned with life as a soldier and quickly realizes the true nature of war in all its bloodiness and brutality.