The Iron Brigade was, according to one account, "the most famous brigade in the entire Union Army" during the Civil War (as approvingly cited by Robert Nesbit in his seminal history of Wisconsin). Alan T. Nolan's brisk study of the Brigade shows why this accolade is deserved.
Comprised largely of Wisconsin regiments, along with regiments from Indiana and Michigan, the Brigade slogged up and down the Peninsula for over a year, before becoming, at Gettysburg, the anvil on which A.P. Hill's Confederate hammer pounded. The Brigade's losses, between McPherson's and Seminary Ridges, were horrific: 2/3 loss of manpower, including 80% of the Michigan regiment. But the Brigade maintained discipline throughout, retreated in orderly fashion, and inflicted massive losses on the enemy. Though the Brigade suffered a tactical defeat, it not only took the fight to the Confederates, it, in Nolan's words, "determined the matter, by their dogged, desperate fighting, which had permitted Federal possession of the key ground and had purchased the time for the Army of the Potomac to concentrate." Gettysburg may have been won as much by the the Iron Brigade as by the later, more storied repulse of Pickett's Charge.
Nolan doesn't quite explain -- perhaps it's simply inexplicable -- just why the Brigade managed such fearless devotion to a very bloody cause. It's probably not irrelevant that the soldiers were all from the Western frontier (at least, by the geography of the day). Draw from that whatever conclusions one will -- regional solidarity probably counted for something, along with acquaintance with physical hardship. John Gibbon, it should be noted, took early command and shaped the Brigade into an indomitable fighting force. An artillerist by training, Gibbon proved an adept motivator, to which the Brigade's esprit de corps owed much; Nolan thus portrays as Gibbon as a highly competent commander. Gibbon subsequently found himself truly in the West, and commanded one of the columns chasing down Sitting Bull and Crazy Horse at Little Big Horn. Whatever skills served Gibbon well in the Eastern Theater of the Civil War may not have translated intact to the Plains. In any event, his desultory efforts to track down the Sioux after Custer's defeat came to naught, and the successful completion of that task fell to the more heterodox Nelson Miles.