Exactly! For anyone curious, here's 2 minutes of clicking on Wikipedia: https://en.wikipedia.org/wiki/South_Carolina_Declaration_of_Secession#Synopsis

The General Government, as the common agent, passed laws to carry into effect these stipulations of the States. For many years these laws were executed. But an increasing hostility on the part of the non-slaveholding States to the institution of slavery, has led to a disregard of their obligations, and the laws of the General Government have ceased to effect the objects of the Constitution.

It was a hundred percent about slavery, the entire time, and any "states' rights" or "heritage" stuff is propaganda that white supremacists have put out to try to recruit more white supremacists to their cause of white supremacy

"War of Northern Aggression", it was aggression against slavery