Why did the U.S. Civil War start in 1861?

This paper will be based on a topic "Why did the U.S. Civil War start in 1861? However, the paper must be an argumentative paper so you need to prove your thesis question. The topic MUST BE APPROVED by the professor. A working title/thesis question should be submitted by the 2nd week of class. Your work must be 10-12 pages in length (not counting cover page or reference/bibliography pages), 12-point font double spaced, and cited using Chicago style documentation with footnotes. (Chicago style is the required style in 4000 level HIST courses so it is strongly advised that you learn how to use it in this course.
I would like to go with "Why did the U.S. Civil War start in 1861?" as my Thesis statement