In America, we look at places such as Iraq and Yugoslavia in horror and wonder. How can neighbors, who live in the same communities for years, suddenly rise up and kill each other?

So, it’s disturbing to realize that Americans may not be completely immune from such madness. Such a thing once happened here in Missouri.

I’ve just read T.J. Stiles’ excellent 2002 biography Jesse James, Last Rebel of the Civil War. It’s the story if a robber with a taste for publicity, of course. But it’s also the story of Missouri in the years during and after the Civil War, a time when our society disintegrated into fratricidal chaos, and we behaved much like Iraqis and Yugoslavians at their worst.

Mr. Stiles tells how people from farms and small towns let hate take root and grow, and overwhelm the decency and friendship that had joined them together in their churches and meeting halls.

In most of the nation, the Civil War was fought by marching armies. There were fixed battles in Missouri too, but here the war turned much more personal. Missouri was a border state, and its people were closely torn between those who favored slavery and emancipation, Confederacy and Union. In Missouri, the Civil War was a fight between neighbors. They formed themselves into guerrilla bands, called bushwackers on the Confederate side, and locally-raised Union militia.

They practiced a home-grown form of ethnic cleansing, based not on religion, but on one’s feelings toward the union or slavery. They killed people they knew personally, riding in bands to a neighbor’s farm, calling him out and shooting him.

We had our own version of Yugoslavia’s Srebrenica massacre. In 1863, Missouri bushwackers, Frank James among them, rode across the border to the unionist town of Lawrence, Kansas. “Kill,” ordered their commander, William Quantrill. “Kill and you will make no mistake. Lawrence should be thoroughly cleansed and the only way to cleanse it is to kill. Kill.”

“They killed,” Mr. Stiles writes. “They shot every man and boy they saw. They pulled them out of cellars and attics, knocked them off horses and executed them in front of their families. They clubbed them, knifed them, stole their money and valuables, burned their homes and businesses. Black and white, ministers, farmers, merchants, schoolboys.”

A band of bushwackers, stopped a train in Centralia, Mo., and found 23 unarmed union soldiers headed home on leave, some of them recovering from wounds. The bushwackers ordered them to strip, then shot them dead.

Missourians committed torture. The Union militia visited the James farm, and strung the boys’ stepfather up by the neck, until he told them where his son and fellow guerrillas were hiding.

In 1863, political cleansing became official policy. Union generals in western Missouri ordered bushwackers’ families to pack up and leave. Militiamen rounded up women relatives left at home by bushwackers and placed them in a Kansas City jail. Several died when the rickety building collapsed. Eventually, every rural resident of Cass, Jackson and Bates counties along the Kansas border was ordered out, and union troops marched through burning farms and killing livestock.

Bushwackers lived off the land, which often meant by robbing people. And that’s where Jesse and Frank got their start.

In this atmosphere, the Civil War in Missouri didn’t end with Appomattox. It continued for several more months, as returning bushwackers and unionists settled personal scores. Resentment built as former rebels were denied the right to vote. The Ku Klux Klan arrived.

Into that atmosphere emerged the James gang, master train robbers and perfectors of the daylight bank robbery. Jesse, an inveterate letter writer, teamed up with a former rebel officer turned journalist. Together they concocted the public image of an oppressed son of the South turned daring Robin Hood, stealing from the Yankee oppressors.

It was never true. The James boys spent their loot, they didn’t give it away, and they eventually robbed southerners as well as northerners.

Jesse lived by violence and died the same way; shot in the back of the head by a buddy seeking reward money.