(i) that slavery would not just "go away," as the Founders had hoped, and

(ii) that slavery was the foremost of several key issues dividing the nation into sections and fostering sectional competition. The Missouri Compromise also sought to define zones of free states and slave states, postponing the ultimate resolution of the crisis.

(i) Popular Sovereignty, the invention of Democrats Lewis Cass of Michigan and Stephen A. Douglas of Illinois, who threw the issue into the hands of the people of each would-be state. Proposed by Douglas as the core of the Kansas-Nebraska Act of 1854, this theory was discredited by the catastrophic strife -- a precursor of the Civil War itself -- that tore Kansas apart in the 1850s.

(ii) Slavery as Property Right, the brainchild of Chief Justice Roger B. Taney of Maryland, who declared a slaveowner's interest in his slaves to be like any other property right and denied African-Americans any status as citizens entitled to rights under the Constitution. Taney's goal was to elevate the issue to a nonpolitical, constitutional level and dispose of it by an "authoritative" interpretation of the intent of the framers of the Declaration of Independence and the Constitution. Taney set forth his version of this theory in Dred Scott v. Sandford (1857), which has been reviled ever since, not only as the single worst decision of the U.S. Supreme Court, but also as an unintended catalyst of sectional strife that culminated in the Civil War.

(iii) "Putting Slavery in the Course of Ultimate Extinction"- the position of moderate Republicans such as Abraham Lincoln of Illinois. Lincoln insisted that he did not want to tamper with slavery where it had taken root, but wished to prevent its expansion (hoping that slavery would die out if it could not grow). He offered this position several times in the 1850s, most notably in his "House Divided" speech of 1858. In 1858, when Lincoln challenged Douglas's bid for re-election to the U.S. Senate , they searchingly discussed all three proposals throughout Illinois in the classic "Lincoln-Douglas Debates."

It was a war whose objectives evolved as the struggle evolved. For the Union, it began as a war to preserve the Union and the authority of the government in Washington. But it eventually became a war to destroy slavery, the foundation of the way of life that led the South to attempt to leave the Union. For the Confederacy, it began as a contest to establish the Southern states' right to leave the Union and to preserve their way of life; it evolved as a war of survival and a desperate defense against invasion.

The war reached into society in the Union and the Confederacy. It forced the people of both sides to face the horrors of war by showing them (through the photography of Mathew Brady and his collaborators) what war really looked like, and by the extraordinary carnage the war caused. It imposed privations, chiefly on the people of the Confederacy. It led to advances in ideas about sanitation, medicine, social services. It fostered a new, vigorous, and at times arrogant nationalism in the Union -- what Robert Penn Warren termed the "Treasury of Virtue" that could excuse any national excess and forgive any national sin. By contrast, in the former Confederate states, defeat and surrender fostered among Southerners an ironical perspective on the glittering , successful American experiment -- what Warren called the "Great Alibi," excusing racism, discrimination, poverty, and corruption. (Warren's The Legacy of the Civil War, first written in 1961, remains the best short discussion of its subject.)

The shape of the war, as it evolved from 1861 to 1865, is relatively simple. At the outset of the war, both Union and Confederate commanders believed in the old military adage: "To conquer the enemy, you conquer the enemy's capital." Consequently, both Union and Confederate forces lost many casualties and fought dozens of bloody, inconclusive battles over Washington, D.C., the Union capital, and Richmond, Virginia, the Confederate capital. By the middle of the war (1862 and early 1863), some Confederate commanders -- notably James Longstreet -- advocated defensive war, by which Union forces would have to reconquer the seceded states, acre by bloody acre. By contrast, Union commanders such as Ulysses S. Grant and William T. Sherman intended to make the war a full-scale struggle of peoples and resources; they proposed both to defeat Confederate armies in pitched conventional battles and to destroy Confederates' ability to make war. Union victories in July 1863 in Vicksburg, Mississisippi (in the west) and Gettysburg, Pennsylvania (in the east) indicated that the turning-point had been reached. From then on, the Union armies and commanders grew ever more confident that victory was only a matter of time and treasure. The battles of 1864 and 1865 were among the most horrific the world had yet seen, providing a grim foretaste of what people's war would look like should it ever break out on a global scale. These conflicts devastated the South, leaving wounds that would not heal for generations -- and that ambitious, selfish politicians sought to keep open for generations more.

But the freeing of the slaves was not simply the work of President Lincoln. The slaves did not stand idly by as the war was fought. They played critical -- even central -- roles in their own liberation, both before and after abolition and the destruct ion of slavery became central war aims for the Union. Freed slaves and free African-Americans for the first time were allowed to wear their country's uniform and bear arms in its cause, which truly became their own. Indeed, in many cases throughout the Confederacy, the slaves emancipated themselves without waiting for the assistance of Union armies.

Reconstruction was a period in which African-Americans showed that they could govern themselves and take part in public life alongside their former owners and oppressors. And yet the critical factors in Reconstruction's short-lived success were not the Constitution's new amendments, nor the newly-enfranchised freedmen, not the nation's professed commitment to the principles of Union, victory, and equality. The sole effective guarantors of the success of Reconstruction were the Union occupation forces in the former Confederate states. And Reconstruction was about to be cut off with brutal abruptness.

In 1876, the Democrats apparently captured the Presidency. Most observers agreed that a Democratic victory would bring a swift end to Reconstruction. But the triumph of the Republican ticket brought the same result -- the withdrawal of Union occupation forces, the recapture of Southern states' governments and politics by former Confederates and Confederate sympathizers, and the abandonment of the freed slaves to the "tender mercies" of their former owners.

How did this happen? At first, it appeared that the Democrats had amassed a modest electoral majority. Republicans immediately charged that voting fraud in three Southern states had diverted nineteen electoral votes from the Republican to the Democratic ticket; shifting those nineteen votes would give the Republicans a one-vote margin of victory in the electoral college. In a murky and still-controversial series of investigations and deals, a special electoral commission composed of eight Republicans and seven Democrats awarded the disputed electoral votes to the Republicans. In 1955, C. Vann Woodward published a pathbreaking study, Reunion and Reaction, in which he offered the first close interpretation reconstructing the complex web of subterranean political and economic transactions that resulted in the Republican victory and the "Compromise of 1877." Several later historians have disputed many of Woodward's findings, and some have even denied that a sectional "Compromise of 1877" ever took place`. Whatever the case, however, Union armies were withdrawn, and (as Eric Foner, the greatest historian of the period, has noted), Reconstruction remained "America's unfinished revolution."