Erwin earned his law degree from the University of Missouri Law School, and is a veteran of the United States Army. Guerillas in the Civil War in Missouri is the first book Erwin has published. Erwin writes a chronological narrative that tells the basic story of the guerilla war in Missouri, and how it affected the lives of Missouri civilians during the Civil War. The Civil War in Missouri was inextricably linked to the Civil War in Kansas, and Erwin also tells the story of Kansas’s effect on the guerilla war in Missouri in this work.