Maybe not a positive example by it is often said that "Uncle Tom's Cabin" by Harriet Beecher Stowe was one of main catalysts of the American Civil War. When Lincoln met her, he said "Here's the the little lady who started the great war."
Beyond its now-problematic portrayals of race, the book got ordinary people talking about the horrors of chattel slavery in the US in a way they had not before. It was talked about everywhere and made abolition more palatable for ordinary people.