The troop of cavalry had been organized three months before, the very day that Georgia seceded from the Union, and since then the recruits had been whistling for war. The outfit was as yet unnamed, though not for want of suggestions. Everyone had his own idea on that subject and was loath to relinquish it, just as everyone had ideas about the color and cut of the uniforms. (1.136)
Early in the novel, everybody is eager for war, which they think will be glorious and awesome. The irony is that war is horrible and they'll all regret wanting it.
"Land is the only thing in the world that amounts to anything," he shouted […] "'Tis the only thing worth working for, worth fighting for—worth dying for!" (2.115)
Gerald says land is worth fighting and dying for. This makes it seem like the war is about fighting and dying for land, or protecting one's home, but in fact the war is about protecting the right of rich jerks like Gerald to own slaves.
Oh why couldn't she feel like these other women! They were whole hearted and sincere in their devotion to the Cause. They really meant everything they said and did. And if anyone should ever suspect that she— No, no one must ever know! (9.79)
Scarlett doesn't care about the Cause; she's not interested in the war. This is somewhat convenient, since it means the novel never really has to think that hard about what the war is or why it's being fought. Scarlett's lack of patriotism allows the novel not to examine the patriotism too closely.
"All wars are in reality money squabbles. But so few people ever realize it. Their ears are too full of bugles and drum and fine words from stay-at-home orators." (12.75)
Rhett's words seem like cynical realism, but can you find some truth to them? Slavery is an economic system, after all, and secession by Southern states threatened the existing unified economy.
As she looked, two streams of blood crept across the shining floor, one from his face and one from the back of his head.
Yes, he was dead. Undoubtedly. She had killed a man.
[…] suddenly she was vitally alive again, vitally glad with a cool tigerish joy. She could have ground her heel into the gaping wound which had been his nose and taken sweet pleasure in the feel of his warm blood on her bare feet. She had struck a blow of revenge for Tara—and for Ellen. (26.22-24)
Scarlett herself is a fighter in the war, killing a Union soldier. The murder is presented as joyful revenge and as a moral good. The only good Yankee is a dead Yankee in this book.
"I don't know why we fought and I don't care," said Scarlett. "And I'm not interested. I never was interested. War is a man's business, not a woman's." (29.32)
Scarlett says war is man's business, but she herself killed a man, essentially in the war. As often happens with Scarlett, she seems to take on a male role while disavowing it. She provides for her family and works in the mills and even fights in the war, but none of this ever quite amounts to her actually questioning the role of women overall, or really even her own role as a woman.
How dared they laugh, the black apes! How dared they grin at her, Scarlett O'Hara of Tara! She'd like to have them all whipped until the blood ran down their backs. What devils the Yankees were to set them free, free to jeer at white people! (35.5)
The war and the Yankees are here linked pretty directly to racism. The evil of the war is that it upsets the racial caste system.
"And if they give the n****es the vote, it's the end of us. Damn it, it's our state! It doesn't belong to the Yankees! By God, Scarlett, it isn't to be borne! And it won't be borne! We'll do something about it if it means another war. Soon we'll be having n***** judges, n***** legislators—black apes out of the jungle—" (37.18)
This rather upends Rhett's statement that the war is about money. Tommy clearly says he is ready to have another war for specifically racist reasons. The terrorist violence of the KKK, a continuation of war by other means, is based on refusing to allow black people to gain political power. That is what the Civil War was based on as well.
"He—well, we figure he died like a soldier and in a soldier's cause." (39.10)
Gerald died after refusing to sign a loyalty oath to the Yankees. The fact that this was seen as dying in a soldier's cause indicates the way that the novel sees the Civil War continuing even after the actual fighting is over. The South is still fighting the North… and it doesn't necessarily lose. Which the novel sees as a good thing.
To them she had done worse than murder her father. She had tried to betray him into disloyalty to the South. (40.9)
In the aftermath of the war, loyalty to the South is seen as distinct from, and incompatible with, swearing loyalty to the federal government. The Union may have won the war, but the novel suggests the South didn't accept the victory for a long time.