How did the issue of slavery become a cause of the civil war?

Answer 1

The slavery problem had remained an American issue since the ratification of the US Constitution. Part of the reason that the Civil War was fought was the election in 1860 of Republican Abraham Lincoln. His party was against slavery and although Lincoln promised to allow slavery to exist where it already was, it added to the South's belief that eventually attempts to ban slavery would continue and /or new territories in the US, would possibly add to the in balance between slave States and "free States'.

This fear by Southern politicians and wealthy plantation owners that depended upon slavery to work the cotton and tobacco fields, was certainly one major reason that slavery became an issue in bringing upon the US Civil War.