Always remember that they are a country with slavery enshrined in their constitution. That is they fully support it in certain cases. Should tell everything about their justice system.
That intentional backdoor has been used to oppress and re-enslave America's black population via unjust laws, incarceration and forced labor ever since that bloody civil war ended. There's a reason prisons in the South make their (predominantly black) inmates pick cotton, and it isn't because that's cost effective. Prison labor is a direct reinstatement of the former slave labor system, and many prisons in the South were formerly slave plantations.
https://www.battlefields.org/learn/primary-sources/declarati...
That was just the first result from searching for "letters of secession"
Saying the civil war is not about slavery because the invasion was about responding to Confederate belligerence is like saying that someone who died with Covid-19 actually died from heart failure. You might be technically correct (most people's hearts fail when they die), but it's at best pedantic and at worst disingenuous.