If you think the United States is polarized now, consider the unbending antagonisms of 140 years ago, when the states were disunited, as Barnet Schecter shows in his richly detailed and formidably documented history.

		"THE DEVIL'S OWN WORK: THE CIVIL WAR DRAFT RIOTS AND THE FIGHT TO RECONSTRUCT AMERICA" By Barnet Schecter Walker ($27)

The country then was not simply a house divided, North and South, but a house splintered.

Within the Union were Peace Democrats, War Democrats, Liberal Republicans, Radical Republicans, African-Americans, Irish-Americans, workingmen, "Copperhead" supporters of the South, and many others -- each at various times at other groups' throats.

Fortunately for the reader, Schecter (author of "The Battle for New York: The City at the Heart of the American Revolution") makes sense of the bewildering array.

"The worst riots in American history" broke out in New York City on July 13, 1863, barely after the smoke had cleared from Gettysburg.

Walt Whitman called them "the devil's own work," for they turned into four days of looting, arson, lynching and other murder that left 105 dead -- in the official count. The toll almost certainly was more than 500.

Thousands of black people were forced to flee a city that tottered on the brink of collapse as a political and commercial hub.

Although groups developed their own self-serving conspiracy theories as to the cause, Schecter says the riots appeared to be a spontaneous uprising against President Abraham Lincoln's imposition of the first federal draft in the nation's history, with its clause exempting any conscript who could provide a substitute or pay $300, a year's wages for many workingmen.

And the rioters were overwhelmingly workingmen; Irish Catholics too poor to afford the $300 exemption, who would be the ones to serve and whose families would be forced onto charity rolls.

They were encouraged by speeches by New York Democratic politicians sympathetic with the Confederacy. The Irish gangs targeted blacks, but also wealthy, mostly Republican, Protestants, whom they saw as representing a government that would send them to die for slaves who would replace them, at even lower wages, on the docks and in the factories.

It was, they said, "a rich man's war and a poor man's fight." One Peace Democrat (an opponent of "Lincoln's war") charged that with the draft "they offer to buy up white men for three hundred dollars each, about one-third of what a good negro is worth."

However, the riots, layered with elements of racial, religious, ethnic and class conflicts, were about much more than the draft.

They were "a microcosm within the borders of the supposedly loyal northern states of the larger Civil War between the North and South."

The words "supposedly loyal" are a nice touch that gives away the author's skeptical attitude. New York City, long a center of trade with the South, was a hotbed of Confederate sympathizers, and if he is hard on anyone, it is the Democratic Party for being the focus and the voice of that sympathy.

On the other hand, he also recognizes that for the rioters the Republican mayor, George Opdyke, "symbolized both the oppression of the state legislature and the Lincoln administration, while his wealth and business dealings marked him as a profiteer, benefiting from the protracted war in which the poor were dying on the front lines."

Of the 1 million people living in New York, at least half were poor or working-class. Parts of lower Manhattan were such a fetid pigsty, you may nearly gag reading about them. And living within hailing distance of all that were war profiteers growing rich from selling "shoddy" -- defective or substandard equipment -- to the military into which these men were to be drafted.

Yet nothing is static. By 1872, Liberal Republicans were allying with northern Democrats. Horace Greeley, longtime editor of the New York Tribune (a Republican newspaper) and presidential candidate in 1872 on a Liberal Republican/Democratic ticket, embodies the shifting alliances of the middle decades of the 19th century.

After a long career of speaking out on behalf of blacks, Greeley began criticizing their role in Reconstruction. Once a friend of the working class, he became estranged from it.

The bulk of this excellent book is devoted not to the riots themselves, but to the tremendous social unrest that led up to and flowed from them, specifically, the turmoil of Reconstruction.

Under the long shadow of the riots fell a century of repression of black civil rights and of harsh treatment of labor protests.