While there were assuredly many causes/reasons/motivations for the explosion of the Civil War, it is important to remember that the tensions that caused it were building up over decades. And the tension buy and large revolved around slavery.^1

These events included the Missouri Compromise, which prohibited slavery north of the 36'30' parallel in 1820. This Act was favored by many on both sides of the slavery issue. However, this legislation was repealed by the Kansas-Nebraska Act in 1854.^2 This Act decided that "popular sovereignty" would be in place for these territories. This opened up the two territories for settlers in the territories to decide by a vote whether or not to allow slavery in the given territories. This resulted in "Bleeding Kansas", where settlers moved to Kansas in a mad dash, some for and others against slavery. These differing settlers battled it out in a quasi-war for the territory where an estimated 200 people died.^3 This was a huge sign to the government, and Americans in general, that the slavery question was not going to be decided by peaceful legislation. A decision would have to be made: either allow or prohibit slavery. And with the election of Abraham Lincoln, many in the South believed that the new president would prohibit their beloved institution. Thus the secession of South Carolina and the following southern states, and the beginning of the American Civil War.

I realize I haven't necessarily answered your question and here's why. The answer to your question is there were no other "major" causes for the American Civil War. At least none that aren't connected to slavery. Whether it was "states' rights", westward expansion of slavery, Lincoln's election, or whatever cause one puts on the table, slavery lies at the bottom.

I say all this to make one point: there may be many causes of the American Civil War, but none of these can be separated completely from slavery. Your post doesn't say otherwise; but too often people will try to find other "big" causes of the war, when in actuality slavery is at the bottom of all of them.

So my answer, as someone who has spent the majority of their undergraduate career studying the Civil War, is that one might find small or large causes for the war that aren't themselves slavery, but if you peel back the layers you will find that slavery, the wretched institution that is was, was the prevalent catalyst for the American Civil War.

[1] Half Slave or Half Free by Bruce Levine (general thesis of his book)

[2] The Missouri Compromise; https://en.wikipedia.org/wiki/Missouri_Compromise

[3] Bleeding Kansas; http://www.britannica.com/event/Bleeding-Kansas-United-States-history