I am not going to argue that slavery was not an issue in the Civil War, but the issue that started the talk about secession was tariffs on goods from Europe received in payment for cotton grown in the South.

Lincoln did not initially want to end slavery. The U.S. government wanted to limit it to existing slave states, and yes, the South objected to that. The Emancipation Proclamation was issued in 1863 out of concern that France and England were preparing to recognize the CSA and start supplying the South with weaponry.

Bottom line, the Civil War could have easily been prevented and perhaps the secession could have also been prevented. Either way, the South would have likely ended slavery in less than ten years. The industrial revolution was making slavery a losing proposition, and it would have been a matter of economic necessity to end it sooner than later.