The diminutive union XII corps found significant success on the field at Antietam. Its soldiers swept through the East Woods and the Miller Cornfield--permanently clearing both of Confederates--repelled multiple Southern assaults against the Dunker Church plateau, and eventually secured a foothold in the West Woods. This important piece of high ground had been the Union objective all morning, and its occupation threatened the center and rear of Gen. Robert E. Lee's embattled Army of Northern Virginia. Federal leadership largely ignored this signal achievement and the opportunity it presented. The achievement of the XII Corps is especially notable given its string of disappointments and hardships in the months leading up to Antietam.

M. Chris Bryan's Cedar Mountain to Antietam: A Civil War Campaign History of the Union XII Corps, July -September 1862 begins with the formation of this often-luckless command as the II Corps in Maj. Gen. John Pope's Army of Virginia on June 26, 1862. Bryan explains in meticulous detail how the corps endured a bloody and demoralizing loss after coming within a whisker of defeating Maj. Gen. "Stonewall" Jackson at Cedar Mountain on August 9; suffered through the hardships of Pope's campaign before and after the Battle of Second Manassas; and triumphed after entering Maryland and joining the reorganized Army of the Potomac. The men of this small corps earned a solid reputation in the Army of the Potomac at Antietam that would only grow during the battles of 1863.

This unique study, which blends unit history with sound leadership and character assessments, puts the XII Corps' actions in proper context by providing significant and substantive treatment to its Confederate opponents. Bryan's extensive archival research, newspapers, and other important resources, together with detailed maps and images, offers a compelling story of a little-studied yet consequential command that fills a longstanding historiographical gap.