Any real scholar can tell you that the tariff was a dead issue prior to the Wah. The government was controlled by the South and Southerners almost its entire history. JQ Adams, Millard Fillmore, Franklin Pierce, Martin Van Buren and Buchanan were its only presidents not from the South and VB, Pierce and Buchanan were completely subservient to the Slavers.
The RAT Rebellion came because the Slavers decided to fight for an Ignoble Cause, under false pretenses and a fundamental lack of understanding of the difference between a Union and a Confederacy clearly laid out in the Federalist.
It was launched almost entirely, if not entirely, in defense of Slavery. The North fought to preserve the Union.
You said: “The North fought to preserve the Union.”
In the sense that it was fighting to protect the TARIFFOCRACY, you are right.