this remains a controversial question.

Why? Because many people don't want to believe that the citizens of the southern states

were willing to fight and die to preserve a morally repugnant institution.

There has to be another reason, we are told. Well, there isn't.

The evidence is clear and overwhelming. Slavery was, by a wide margin, the single most important

cause of the Civil War -- for both sides. Before the presidential election of 1860,

a South Carolina newspaper warned that the issue before the country was, "the extinction

of slavery," and called on all who were not prepared to, "surrender the institution," to act.

Shortly after Abraham Lincoln's victory, they did.

The secession documents of every Southern state made clear, crystal clear,

that they were leaving the Union in order to protect their "peculiar institution" of slavery

-- a phrase that at the time meant "the thing special to them." The vote to secede was 169 to 0

in South Carolina, 166 to 7 in Texas, 84 to 15 in Mississippi. In no Southern state was the vote close.

Alexander Stephens of Georgia, the Confederacy's Vice President clearly articulated the views

of the South in March 1861. "Our new government," he said, was founded on slavery. "Its foundations are laid,

its cornerstone rests upon the great truth that the Negro is not equal to the white man;

that slavery, submission to the superior race, is his natural and normal condition."

Yet, despite the evidence, many continue to argue that other factors superseded slavery

as the cause of the Civil War.

Some argue that the South only wanted to protect states' rights. But this raises an obvious question:

the states' rights to what? Wasn't it to maintain and spread slavery?

Moreover, states' rights was not an exclusive Southern issue. All the states -- North and South --

sought to protect their rights -- sometimes they petitioned the federal government, sometimes

they quarreled with each other. In fact, Mississippians complained that New York had too strong a

concept of states' rights because it would not allow Delta planters to bring their slaves to Manhattan.

The South was preoccupied with states' rights because it was preoccupied

first and foremost with retaining slavery.

Some argue that the cause of the war was economic. The North was industrial and the South agrarian,

and so, the two lived in such economically different societies that they could no longer stay together.

Not true.

In the middle of the 19th century, both North and South were agrarian societies. In fact,

the North produced far more food crops than did the South. But Northern farmers had to

pay their farmhands who were free to come and go as they pleased, while Southern plantation

owners exploited slaves over whom they had total control.

And it wasn't just plantation owners who supported slavery. The slave society was embraced by

all classes in the South. The rich had multiple motivations for wanting to maintain slavery,

but so did the poor, non-slave holding whites. The "peculiar institution" ensured that they

did not fall to the bottom rung of the social ladder. That's why another argument

-- that the Civil War couldn't have been about slavery because so few people owned slaves -- has little merit.

Finally, many have argued that President Abraham Lincoln fought the war to keep the Union together,

not to end slavery. That was true at the outset of the war. But he did so with the clear knowledge

that keeping the Union together meant either spreading slavery to all the states

-- an unacceptable solution -- or vanquishing it altogether.

In a famous campaign speech in 1858, Lincoln said, "A house divided against itself cannot stand."

What was it that divided the country? It was slavery, and only slavery. He continued:

"I believe this government cannot endure permanently half slave and half free... It will become

all one thing, or all the other." Lincoln's view never changed, and as the war progressed,

the moral component, ending slavery, became more and more fixed in his mind.

His Emancipation Proclamation in 1863 turned that into law.

Slavery is the great shame of America's history. No one denies that.

But it's to America's everlasting credit that it fought the most devastating war in its history

in order to abolish slavery.

As a soldier, I am proud that the United States Army, my army, defeated the Confederates.

In its finest hour, soldiers wearing this blue uniform -- almost two hundred thousand of them

former slaves themselves -- destroyed chattel slavery, freed 4 million men, women,

and children from human bondage, and saved the United States of America.

I'm Colonel Ty Seidule, Professor and Head, Department of History at the United States

Military Academy, West Point for Prager University.