Sadly, it is hard for us today with our highly Secularized culture to understand the importance of Christianity in the way the Civil War played out for nearly all Americans in the 1860s.  Morally it was very hard for Americans to want to kill other Americans.  Southerners of course would quite naturally want to fight to fend off Northern aggression.  But for Northerners, who personally knew of slavery mostly through stories and reports of others, the issue of slavery was largely a moral abstraction.  It is easier to find cause to go to war for the defense of one's home and land when they come under attack.  The South certainly felt that this was the case for them. It is more difficult to find the will to go to war for moral abstractions.

However the Second Great Awakening provided exactly the required sense of moral commitment to those Northerners who took up arms.  To Christian Americans, the nation had always been a divine experiment, a model of how it was possible for a people to live freely in a post-feudal society in which a perfect God – not a sinful and blemished man – stood over them as director and enforcer of life. To such Christians it was imperative therefore not to lose that relationship with God lest the Republic under God should fail and bring down man's great hope for democracy with it, possibly discouraging any further attempts at democracy, ever.
Appropriately enough, while Southern soldiers sang romantically about the land of Dixie that they were defending, Northern armies went into battle singing The Battle Hymn of the Republic,¹ a call to join with God in his mighty hand of judgment on the nation.  Through the horror of the war that challenged America, God's Truth, God's Will, would prevail.

Mine eyes have seen the glory of the coming of the Lord;
He is trampling out the vintage where the grapes of wrath are stored;
He hath loosed the fateful lightning of His terrible swift sword:
His truth is marching on.

Glory, glory, hallelujah!
Glory, glory, hallelujah!
Glory, glory, hallelujah!
His truth is marching on.

I have seen Him in the watch fires of a hundred circling camps,
They have builded Him an altar in the evening dews and damps;
I can read His righteous sentence by the dim and flaring lamps:
His day is marching on. ...

He has sounded forth the trumpet that shall never call retreat;
He is sifting out the hearts of men before His judgment seat:
Oh, be swift, my soul, to answer Him! be jubilant, my feet!
Our God is marching on.

¹The words were written by Julia Ward Howe (using the melody from an old Methodist hymn "Say Brothers" – or more popularly at the time, "John Brown's Body") and published in the February 1862 edition of The Atlantic Monthly.

The election of Lincoln was the signal for the Southern states to begin to announce their secession from the Union.  On December 24th (1860) South Carolina was the first Southern state to announce its withdrawal. Six others (Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas) soon joined South Carolina and on February 4, 1861 they announced at a meeting in Montgomery, Alabama, the creation of the Confederate States of America.  There a provisional government was established, with Jefferson Davis as the provisional Confederate president.

Initially the moral claim of the new Confederacy was that it was simply confirming the basic rights of the states, rights that reached back to Madison and Jefferson, rights that they claimed former Federalists and contemporary Unionists had been stealing from them.  And indeed, the Confederacy was built loosely so that the states did indeed seem to be nearly fully sovereign and the Confederacy simply a coalition of rather independent states.

Yet there were strong forces holding the Confederacy together. Actually, the very looseness of the Confederacy required as a matter of extreme necessity a strong, commanding hand to hold it together.  And that hand appeared in the form of Jefferson Davis, the Confederacy president. In many ways, the struggle of the South to secure its independence militarily required him and his administration to take on almost unlimited powers.

But holding the Confederacy together was the even more powerful ingredient: fear White Southerners had of their Black population – both free and slave.  The Black population was growing at such a rate that Whites were terrified by the thought of being outnumbered in their Southern homeland by Blacks.  The preventing of the spread of slavery into the new Western territories – as Lincoln and most of the North had committed themselves to doing – would imprison the South in a confined world over which they feared they could soon lose control.

Paranoia and thoughts of anti-White conspiracy coming from multiple directions gripped at the Southern imagination, forging Southerners into a tight bond. But that bond would soon deprive them of the real sense of freedom that they claimed they were achieving in breaking from the Union.  The South became an oppressive land, whose laws and cultural vigilance tightened down on society.  Free Blacks living in the South soon found themselves under the threat of being forced into slavery. And war fever in the South demanded that any Northern Blacks captured in battle (those not just killed outright), or simply captured as farm workers in the process of the Southern armies advancing across the land, would be carried off into Southern slavery.

As both Jeff Davis and his vice president, Alexander Stephens, put it, Blacks by their very inferior nature were intended by God to thrive only within the context of eternal servitude to the superior race of Whites.  Enslavement of any and all Blacks was actually a necessary part of the advance of civilization. This credo was thus the real glue holding the Confederacy together.