I would venture to say that this book helped the Civil War along because it told a cruel story about runaway slaves and the harsh labor conditions of the field workers. The house slaves, while treated better than the field slaves, were often chosen due to their paler skin and pretty faces. They were often mistresses to the plantation owner, and gave birth to light skinned offspring who often were recognized as the landowner's children and cared for as such.
The Northerners were outraged by such atrocities and were quick to point the finger at the Southerners for being immoral. Of course, Jesus said in the Bible of the woman who was accused of Adultery, "Let those who are free from sin cast the first stone toward this woman."
While many slave holders in the South were cruel and did treat slaves in horrid manners, there were just as many who treated their slaves well. These same slaves chose not to leave after the Emancipation Proclamation and worked on as hired help. They were often the heirs to the land when the landowners died. They became wealthy as a result.
Uncle Tom's Cabin showcased the worst stories, thus inciting anger and human rights activists to arms.