Uncle Tom's Cabin and the Civil War

Stowe and Lincoln

Legend has it (as reported by her son some years later) that when Harriet Beecher Snow met Abraham Lincoln after he was president in 1862, he stated to her, "So you're the little woman who wrote the book that started this great war."  Whether true or not, this statement points to the influence this book had, especially in the North; but also as a mechanism of polarization with the South on the theme of slavery. 
The book was published as a book in 1852, and seen previously in magazines.  Stowe says one of her motivations for writing the book was the passage of the Fugitive Slave Act of 1850. 
300,000 copies of the book were purchased in the North before the war.  In many parts of the South the book was illegal.  It was even more popular in England.  Even if England's political leaders had wanted to enter the war, the public opinion in England would have been very much against them, partly due to this book. 
Of course their were many causes for the war.  What this book did do was put a face on slavery.  Through the characters presented, people could see slavery.  Stowe especially talked about its effects on family groups.  It may very well be that we are seeing the effects of this disruption even today.  Another theme in Stowe's book is that through Christianity, you didn't have to give yourself to the hate which slavery could very well cause. 
Hardened abolitionist didn't think the book went far enough in crying for immediation abolition.  Other northerners saw it as a triumph for the human aspects it put on slavery.  Southerners thought it was for the most part outright lies. 
Stowe contended that even though the actual characters were fictional, they were based on  real life stories she had heard of. 
When Stowe wrote a defense of her book, "The Key to Uncle Tom's Cabin" she was even more staunch in her call for abolition.  
http://mmboebillywardle.blogspot.com/2014/08/book-review-uncle-toms-cabin.html