WAS THE WAR BETWEEN THE STATES ABOUT SLAVERY?

Yes, of course, the War Between the States was about slavery, among other things.

The larger issue was sectionalism.  The United States by 1860 was divided into 3 distinct sections:  the industrial North, the agrarian South, and the expanding West.

SECTIONALISM:  Each section of the nation had very different lifestyles, economies, political viewpoints and needs.  The economic system of the agricultural South depended on slavery. The North's economy no longer did.  

THE TARIFF:  The North, which exported goods, wanted a protective tariff on imported goods to protect its manufacturing or industrial base from foreign competition.  The South, which depended largely on imported goods, hated the tariff.  As far back as 1828, the Congress passed a high tariff to protect goods manufactured by Northern industries.  The South hated it so much they called it "the Tariff of Abominations."  This conflict continued until the civil war broke out in 1861.

STATE'S RIGHTS:  The argument was really the political argument that could not be solved.  The southern states had always, since before the Constitution was ratified, believed that each state was sovereign and entitled ultimately to set its own political course.  The South viewed the Union as a subordinate thing--agreed upon voluntarily in Philadelphia by the various sovereign states, which could, when necessary nullify unwarranted acts of the national government at will. The North, by contrast, felt that the Union was sacred, ultimate, the final authority in the nation.  These opposing viewpoints came so severe that they could only be decided at terrible places like Gettysburg and Antietam.

Thus, the 3 major issues that caused the War were:
1.  Sectionalism
2.  The Tarrif
3.  Conflict over state sovereignty vs. national soverignty

These were the three sticks of dynamite in the powder keg.  The West was the catalyst that prevented delay in finding a peaceful solution.  New territories were being settled and were applying for statehood.  The balance between free states and slave states was carefully maintained until 1850.  Then Kansas and Nebraska exploded into what really became the real "civil war," as slaveholders and opponents of slavery fought and killed each other there.  So Kansas and Nebraska lit the fuse.

The event that blew the lid off was the unlikely election of Abraham Lincoln in 1860.  Lincoln was a dark horse Republican candidate without a chance of winning the presidency.  Except for two things.  The Democrats chose Stephen A. Douglas of Illinois as their candidate and Douglas was unacceptable to the southern states.  So southern delegates walked out of the Democratic convention and selected John C. Beckenridge to run as a "Southern Democrat." Thus, the Democrats had their vote divided two ways.  Finally, there was a fourth candidate, John Bell of Tennessee, who voiced no clear stand on the urgent issues of his day, declaring himself only to be "for the constitution and the union."  

Come election day 1860, the electoral vote was splintered like a barn door.  Douglas won 12 electoral votes, Breckenridge got 72, Bell 39, and Lincoln 180.  The popular vote was just as scattered:  Lincoln had 39.8 percent.  Breckenridge had 18.1 percent.  Douglas had only 29.5%, while Bell received 12.6%.  The most divided election in American history.

And Lincoln won without carrying a single southern state.  If you look at the election on a map, there is a line running along the southern boundaries of Illinois, Indiana, Ohio and Pennsylvania.  Lincoln did not carry a single state south of that line.

When it was announced that Lincoln was the new president, the South exploded.  Legislatures were called into special sessions and southern states began to secede.  This was, I believe, irrational and suicidal; nevertheless, this is what they did.

So, was the war about slavery?  Yes, of course it was.  And it was also about state's rights, the tarrif, balance of power in the new western states--all the clouds forming under the horizon of intense sectionalism.

I would contend that the causes of the war were different from the course of the war. After Lincoln called for 75,000 volunteers to invade the South and "put down the rebellion," the course of the war became to protect the homeland.  Each southern state's objective became, not the preservation of slavery, but keeping the invading federal armies out of Virginia, South Carolina, Georgia....

Go to any battle line in the Confederate army and ask the common soldier, "Why are you fighting?"  I doubt you would get anyone to say, "Why, I'm fighting to preserve slavery."  No, sir.  Here is what you would get:  "I'm fighting for my home."  Or, "I'm fighting for my state."  Or, "I'm fighting to protect my rights."  Perhaps, "I'm fighting to preserve our way of life."  Or, as one Alabamian put it when a Union soldier asked him why he was fighting:  "I'm fightin' because you are down here."

Listen to General Lewis Armistead, one of Pickett's Brigade Commanders at Gettysburg.  In the minutes before the fateful charge Armistead shouted to the 5,000 Virginians in his command:  "For your homes, for your wives, for your sweethearts....For Virginia!"  And the chorus swelled behind him in reply, "For Virginia!"

  No one answered "For slavery!"