No it wasn't. It was part of 3 of them. Four if yous stretch a bit. But the other 7 out of 11 states did not mention slavery as a motivation.
Virginia (the most important state) says they seceded because the Federal government had become tyrannical when it called for an army to subjugate the other states.
The war was not about slavery. The Corwin amendment proves that. The war was about the South trading directly with Europe without Washington DC and the Northeastern robber barons getting their cut of the deal.
This is the most absurd “analysis” I’ve ever heard as to the cause of the war.