The US did not force the southern states into the union. Rather they prevented the tiny minority of slave owners in the country from tearing apart the union.
The revolutionary war was vastly different. No taxation without representation. Because of the distance between north america and England, the colonies could not be represented in England. The colonies had their own powers of local taxation. The government of England pretended to have the power to tax the colonies, and when that pretended power was resisted, the government of England send soldiers and marines to make war on the colonies. Only after the war started did the colonies declare independence.
The southern insurrection first declared their independence, based on slavery, though there was no effort made by the US to end slavery, or tariff, though the tariff at that time was low. Then the insurrection declared war on the US, then made war on the United States. None of those were justified, and accordingly, they could not find a single country in the world to support them, and over 40 regiments of southern men fought against the insurrection.
“The US did not force the southern states into the union. Rather they prevented the tiny minority of slave owners in the country from tearing apart the union.”
Honestly, it’s no use trying to argue with this kind of self delusion.