As stated in the article, slavery did not cause the Civil War (because Lincoln did not even think of the Emancipation Proclamation until well after the war began).
The problem was tariffs that strangled the South’s economy, and they would have done so had the South’s cotton been harvested by free workers on horse-powered or steam-powered cotton picking machines.
The article is incorrect. The original seven Southern states seceded before the tariff was voted on.