Original: In the book, Stowe discusses each of the major characters in Uncle Tom's Cabin and cites "real life equivalents" to them while also mounting a more "aggressive attack on slavery in the South than the novel itself had."
Simplified: In the book, Stowe writes about the important characters in Uncle Tom's Cabin and about people in real life who were like them. Through this book, she writes a more "aggressive attack on slavery in the South than the novel itself had."