As has been discussed here before, the simplistic and intellectually dishonest notion that the WBTS had a single cause (whether that cause be slavery, tariffs, or sectionalism), more often than not reveals one's agenda-driven view of this part of our history. Whether the single view theory comes from a self-righteous academic bent on demonizing the South, or from the descendant of a Confederate soldier attempting to justify the South's secession, single issue causation has become little more than a tug of war for modern political and ideological reasons. Attempting to have a discussion with someone from either view is usually fruitless as they really don't want to be confused by the facts. They have their version of the truth, thank you very much.
With that in mind, I would recommend a piece written by Phil Magness who is a professor of political science at American University. The piece is titled, Did tariffs really cause the Civil War? The Morrill Act at 150
Here's Professor Magness's bottom line:
"A measured and factually grounded take of the tariff issue reveals its dramatic resurgence between 1858-61 as the national political climate collapsed and pre-war sectional divisions reached a fever pitch. The issue directly contributed to those divisions, particularly as it arrived in the Senate during the 'Secession Winter' to add its own havoc to a rapidly growing perfect storm. Though it is not a complete or full explanation of the Civil War itself, it should be viewed as an indicator of the war's complexity. Simplistic, single-issue explanations of large political and military upheavals seldom work under scrutiny, and the tariff is one such sign of how the economic dimensions of secession overlapped and intertwined with the Civil War's moral questions about slavery and political questions about sectionalism." (Emphasis mine.)
You can read the complete piece here.