For most Americans it is all but impossible to imagine a time when murder, torture, and intimidation — terrorism — determined our own elections.

But in the election violence of 1868–1876 during Reconstruction, we can find a homegrown brand of American terrorism that forever mars America’s claims as a political model for the world. We have come a long way from the success of the “Red Shirts” in using terror to overthrow Reconstruction and black political liberty in South Carolina in 1876 to the victory of Barack Obama in that state’s Democratic presidential primary this month. But, as Stephen Budiansky shows in his passionate, frustrating “The Bloody Shirt” (Viking, 336 pages, $27.95), we forget the violence of the 1870s at our peril. A conservative estimate of 3,000 Americans were killed, and countless thousands more maimed, tortured, or rendered homeless during this political reign of terror — often dubbed by the Northern press as the “Southern outrages.” Politics can be war by other means, and the Civil War did not end at Appomattox.

Reconstruction violence, committed by the Ku Klux Klan and its imitators — rifle clubs and small-scale vigilante armies that came to control whole counties and regions — was a major weapon in the white Southern Democratic party’s counterrevolution against the Republican governments established by 1868 in all the ex-Confederate states. Those governments included many black elected officials and enacted numerous progressive measures to expand public education, literacy, land ownership across class lines, and in general more democracy than the South had ever known. This was accomplished through the revolution of black male suffrage, and former slaves embraced their new liberties with zeal and competence. But when federal authority retreated from the scene faster than it had arrived by war, Southern Democrats sought to “redeem” their states for white supremacy by crushing black and white Republican organizations, and no tactic proved more effective than violence. By 1871 Virginia, North Carolina, Tennessee, and Georgia were “redeemed” (legislatures and governorships returned to Democratic party control) and Alabama, Arkansas, and Texas followed by 1873.

Mr. Budiansky’s story is largely that of the vicious violence used in Mississippi in 1875 and in South Carolina and Louisiana in 1871 and 1876 to overthrow duly elected governments rooted in the experiment of racial equality that the Thirteenth, Fourteenth, and Fifteenth Amendments had made possible. Such violence included dragging blacks who had voted or organized as Republicans from their homes and subjecting them to torture and sometimes ritual execution. It also included assassinations of constitutional convention delegates as well as Republican sheriffs and members of state legislatures. Rifle clubs tended to carry out killings and intimidations in the comfort of groups, targeting local politicians and citizens, while their goals were the broader destruction of black civil and political rights and the end of Reconstruction regimes.

Writing self-consciously “popular history,” badly flawed at times by excessive quotation, Mr. Budiansky tells his story through five characters, all heroes of the Reconstruction experiment: Prince Rivers, Adelbert Ames, Albert T. Morgan, Lewis Merrill, and James Longstreet. Rivers, the former slave who had become, during the war, an impressive non-commissioned officer in the First South Carolina Volunteers (the first black regiment), emerges as a trial judge in the violent Edgefield County by 1876. Rivers served heroically against white mobs trying to bring legal proceedings to a situation of guerrilla war. When his town was taken over in the bloody Hamburg Riot of 1876, Rivers, who surprisingly survived with his life, ended up as a carriage driver, the job he had performed in slavery before the war. Rivers makes a good symbol of the revolutionary possibilities of Reconstruction, and his defeat shows its tragedy. Longstreet, the much vilified former Confederate general who joined the Republican party and worked to defend the new egalitarian regimes as a soldier and a businessman, is the least developed of these characters: We encounter him trying to put down a white supremacist insurrection in New Orleans in 1874, but learn little more about him. Morgan was a white carpetbagger, an abolitionist, and a Yankee veteran, who became notorious for marrying a mulatto teacher in the freedmen’s schools. He was elected by black voters to the Mississippi state senate and one of his first legislative acts was to repeal the law against interracial marriage.

Mr. Budiansky’s richest source and most interesting character is Adelbert Ames, the Maine-born former Union general and war hero. Ames was part of the Union occupation of the South during early Reconstruction, eventually moving to Mississippi, where he was elected governor in 1868. A true believer in the experiment of racial equality, he struggled against all odds to make Mississippi what its white population refused to be — a society where black people could vote, hold office, and achieve economic independence. Ames’s remarkable letters and interviews provide some of the best insights into why Reconstruction failed. “Terror caused by murder and threats,” he plainly stated, had brought a “revolution … by force of arms” that returned black people to “an era of second slavery.” Ames thought the white Southerner had “a motive in slandering the reconstructionists because he [himself] committed crime upon crime to prevent the political equality of the negro.” And in resignation, Ames declared: “greed, the father of slaves, was too much for us.”

Unfortunately, Mr. Budiansky lets his characters and their plentiful documents, many of which are simply reprinted as exceedingly long epigraphs for chapters, pass for analysis. The author too often succumbs to writing human-interest history and neglects the demands of interpretation. Quotations are sometimes strung together, 19th-century fashion, and the reader yearns for a more coherent narrative as well as more frequent explication of why all this violence happened as it did. Mr. Budiansky misses opportunities to explain why Ames never got the federal intervention in 1875 he so desperately needed. He also leaves his readers rather confused over distinctions between the grand juries and the Congressional hearings conducted to investigate and prosecute the Ku Klux Klan. In his sea of extraneous detail, Mr. Budiansky does not bother to tell us the results of KKK adjudications: thousands arrested, 3,000 indicted (many pleading guilty to get suspended sentences), 600 convictions, 200 acquittals. Most of those convicted received fines and light jail sentences. Only 65 perpetrators of Klan violence were imprisoned for up to five years in a federal penitentiary in Albany, N.Y.; all were out by 1875, the year the Mississippi “shotgun plan” succeeded.

Mr. Budiansky is effective in showing the sheer depth and virulence of white supremacy in the South. He also captures the nature of the “distorted memories” of Reconstruction in the national narrative that lasted so long in America — making a “victim of the bully and a bully of the victim.” In popular memory we are still crawling out of the dark legend of the benighted South, “oppressed” by “Negro rule” during Reconstruction. Mr. Budiansky also rises to some eloquence in his ending by showing how Hamburg, S.C., vanished even from maps after white men with shotguns massacred local blacks, destroying interracial politics and democracy along with them. “Men die, and towns die,” he writes, “and cruelest of all memories die.”

Today, no one is murdered at our voting polls. But this book and the story it tells should keep us vigilant at protecting our political rights, rendered sacred in the blood of Reconstruction, and beyond.

Mr. Blight teaches American history at Yale University and is the author of the Bancroft prize-winning “Race and Reunion: The Civil War in American Memory” and, most recently, “A Slave No More: Two Men Who Escaped to Freedom, Including Their Narratives of Emancipation.”