Abraham Lincoln credited the author of Uncle Tom’s Cabin with having caused the Civil War. While he was exaggerating, his comment does point to the amount of interest and controversy that this novel generated when it was published.
To understand the historical context in which this book was written, you have to keep it mind that it was published a decade before the Civil War actually began, so America was still practicing slavery in the southern states. To be sure, the issue was being passionately debated everywhere, but at the time it was still legal in many places.
The book was certainly not written in a vacuum. Harriett Beecher Stowe included characters from the entire spectrum of the slavery controversy, representing many different attitudes and beliefs. Enotes has a good historical context section for this book at the link below.