This book showed to horrors of slavery to the northerners by giving them insight into something they really didn't know much about, they knew that slavery was bad, but they didn't realize it was THIS bad.
The underground railroad just freed slaves, it didn't really show the horrors of slavery to the northerners, same thing with slave revolts. Henry Brown exiting the box was influential to a certain degree, but not nearly as much as Uncle Tom's Cabin was.
