In short, this book is long. It is filled with sweeping historical vistas and events, along with plot, plot, and more plot.
Speaking of the plot, in Gone With the Wind it is tied to the history of the Civil War. So you can think of the book as divided into four main, honking sections: Pre-War, Civil War, Reconstruction, and post-Reconstruction.
Before the Civil War, Scarlett O'Hara is a flighty, selfish, sixteen-year-old in Georgia who cares mostly about parties and flirting. She is, however, secretly in love with a neighbor, the intellectual Ashley Wilkes. She discovers he's going to marry his cousin, Melanie, and she's very upset about it. So she decides to get all dressed up and finally tell him she loves him and get him to elope with her, which seems kind of mean to Melanie, but that's the sort of person Scarlett is.
But her plans go awry; Ashley more or less says he loves her but that he's too big a doofus to marry her. (Okay, he doesn't actually use the word doofus but you catch our drift.)
Rhett Butler, a disreputable scoundrel and the novel's hero (more or less), is listening in the room unobserved while Scarlett makes her declaration of love to Ashley, and he teases her about it afterward, because that's the kind of appealing scoundrel he is. Scarlett is angry and upset after she's rejected, and goes off and gets engaged to Melanie's brother, the shy clueless Charles Hamilton. Then the war starts—tragic developments all round.
Second part: Civil War. Charles dies right away from disease in the army, but not before he gets Scarlett pregnant. She is depressed because she has to be in mourning for a husband she didn't even like, plus she's got a kid. She's so down that her parents decide to ship her off to Atlanta for a change of scene, which does in fact cheer her up; she likes the bustle. She stays with her Aunt Pittypat and with Melanie, her sister-in-law and Ashley's wife.
She also consorts and banters with Rhett, who is hanging around and being irritating and sometimes friendly, because he loves her though he won't admit it because he's kind of pitiful. He's also a blockade runner and speculator, and is making money in part because he's not fighting in the war, like all the other able-bodied men. He does eventually ask Scarlett to be his mistress, but she refuses and tells him he stinks.
Anyway, Ashley comes back on leave briefly; he and Scarlett share a significant moment where he sort of declares his love again and asks her to take care of Melanie. While he's not mooning after Scarlett, though, he manages to get Melanie pregnant. With perfect timing, Melly has her baby just as Union forces are invading Atlanta; in the chaos Scarlett has to deliver the baby herself. She gets Rhett to set them on the road to Tara, but he has an attack of something like conscience and leaves to join the army, so he can't take her all the way home.
For the record, Scarlett is not pleased, but manages to get them there herself because she is tough.
Back at Tara, Scarlett's mother, Ellen, has died of typhus, her two sisters are sick, and her father has gone quietly mad from grief. Also, the Yankees have taken just about everything, and most of the slaves have left. (The novel has more sympathy for the hardships of the white slave owners than for the suffering of the people enslaved because the novel is really racist. See "Why Should I Care?" for more on this.)
But Scarlett is tough as nails and twice as mean, and she manages to scrape together food for herself and her family and Melly, who is staying on. She also shoots a passing Yankee raider in the face and takes his money, which becomes the basis for her later fortune.
The war ends; Reconstruction begins. Ashley comes to Tara and ends up staying on, as does another ex-soldier named Will Benteen. However, thanks to the dastardly Reconstruction government and evil Yankee schemers, Scarlett is hit with massive taxes on Tara that she can't pay and that will force her to sell.
She decides to go to Atlanta to find Rhett, who is rich, and who she hopes will either marry her or pay her to be his mistress. But Rhett is in jail for killing a black man (which the novel presents as a virtuous act, because the novel is really racist) and can't get at his money. So Scarlett marries Frank Kennedy, who had been engaged to her sister Suellen. Suellen is understandably upset, but Scarlett uses Frank's money to save Tara, so all's well that ends well, unless you're Suellen.
Rhett gets out of prison and Scarlett borrows money from him to buy mills and set herself up in the lumber business. Frank is upset because he feels it's unseemly for a woman to work, but Scarlett doesn't much care what he thinks. Eventually she employs Ashley as a foreman in one of the mills, and he and Melanie move back to Atlanta.
Frank's especially worried about Scarlett going out alone because the Reconstruction government has encouraged black people to be violent and unruly (we've mentioned the book is really racist, right?). And sure enough Scarlett gets attacked. She escapes, but the Ku Klux Klan rides out to avenge her. It turns out that both Frank Kennedy and Ashley are members of the Klan (that's right, the KKK are supposed to be the good guys here). The Yankees have set a trap for them, though, and Ashley is injured and Frank killed; Rhett Butler saves everybody else through a cunning stratagem.
Everybody in Atlanta hates Scarlett for endangering the men-folk, except for Melanie, who stands by her and is very important in Atlanta society because everyone thinks she is awesome (though she strikes us more as a sanctimonious drip). People also hate Scarlett for doing business with the Yankees. She does business with them anyway, though, because nobody stops her hustle.
Scarlett agrees to marry wealthy Rhett when he proposes (she says she's fond of him, too, not just his money). Rhett still isn't admitting he loves her, but he's quite jealous of Ashley. It's not exactly wedded bliss, but they have a daughter, Bonnie, whom Rhett dotes on.
For Bonnie's sake, Rhett tries to moderate his conduct and get in good with Atlanta society. His efforts are somewhat hindered, however, when Scarlett is caught in an actually innocent friendly embrace with Ashley. Melanie refuses to believe anything was amiss (which it really wasn't) and the town is torn between pro-Scarlett and anti-Scarlett forces.
Jealous Rhett semi-maybe-sort-of-rapes Scarlett, who enjoys it, and it seems like there's a chance that they'll reconcile, but Rhett leaves with Bonnie for New Orleans in a jealous snit. Scarlett discovers she's pregnant; Rhett finally comes back and immediately taunts her and suggests she's be better off if she miscarried, she moves to slap him, misses, falls down the stairs, and has a miscarriage. Not long after, Bonnie gets a horse, falls off it, and then dies attempting a jump. Scarlett and Rhett are horribly grieved, and the death pushes them further apart.
Reconstruction has basically ended now; Southern Democrats are back in control of Atlanta and the South, and black people are being disenfranchised. But while this is supposed to be a good thing (because the book is really racist), all is not happiness and light.
On the contrary, Melly dies from a miscarriage, and Scarlett realizes that she doesn't hate her at all, but loves and relies on her. At the same time, she realizes that Ashley is a loser and she doesn't care about him. And then she realizes she really loves Rhett. Lots of realizations there all at once; have to jam them in since the novel's coming to an end.
Scarlett goes to tell Rhett that she loves him, but he says he used to love her but doesn't anymore, and is going off to travel. She is undeterred, though, and determines to go back to Tara for a break and then to try to figure out how to get Rhett back. Will she? Won't she? Shmoop doesn't know, because that, at long last, is the end. Phew.