Answer:
What it was: Uncle Tom's Cabin is a book/novel that is against slavery. It was authored by Harriet Beecher Stowe (American).
Step-by-step explanation:
Why it was influential: Published in 1852, the novel had a great effect on the attitudes people had towards African Americans and slavery in the U.S. and is said that it "helped lay the groundwork for the Civil War".
Northerner's Reaction: It showed them the violent reality of slavery.
Southerner's Reaction: They said that Stowe was exaggerating her perspective on slavery.