About the causes of civil war

I’m working on a History question and need guidance to help me study.

the causes of the Civil War. Be careful, I want not a random discussion or narration of events, but how those events put this nation on the path to the greatest slaughter in our history. What made the Civil War, as Lincoln declared, “an irrepressible conflict;” in other words, inevitable because of slavery. Yet the great irony of the tragedy was that Lincoln initially made the conflict about preserving the Union, or the US, not slavery. He changed his mind, didn’t he! So, what made the crises of the 1850s so crucial in determining the war? Again, as always, be conceptual, analytical, interpretive in your essays.