While the reading certainly addresses slavery as one of the major factors contributing to the American Civil War, it does not oversimplify the complexity of the time period. Consider page 30 (p. 7 of the PDF), which states that there were two other potential causes of sectional rift--overall cultural differences as well as the industrialization of the North versus the stagnant agricultural economy of the South.
What is the most plausible of these factors? Why do you say so? Do you think this conflict could have been avoided if there was no westward expansion in the colonies?