Charels Sumner personally insulted pro-slavery people, espesially Andrew Pickens Butler. His cousin, Preston Brooks, did not like Sumner saying those things so he beat him unconscieous with a walking cane. Sumner was injured so badly he did not return to work for three years.
Uncle Tom's Cabin informed Northerners of the cruelties of slavery. It was written by Harriet Beecher Stowe. Because of this book, southern slave holders wrote books about how well they treated slaves and how they were helping them. These books did not have the same effect on readers as Uncle Tom's Cabin.
The Missouri Compromise, made by Henry Clay, made slavery illegal anywhere north of the 36, 30 lattitude line. The Missouri Compromise was repealed by the 1854 Kansas-Nebraska Act because the Dred Scott case proved it unconstitutuional.
The census show that the U.S.'s population is 10,037,323. This includes the number of slaves which is 1,529,012. That is 15% of the population. There are barley any slaves in the North. 51% of South Carolina's population is slaves; it is 49% in Louisiana. http://www.civil-war.net/pages/timeline.asp