Dred Scott was a wretched opinion that tried, by judicial fiat, to settle slavery once and for all.
Instead, it further inflamed the debate. It basically said once a slave, always a slave. It introduced the infamous phrase that black people have no rights that white people need respect.
Southern states were seceding before Abraham Lincoln was even sworn in. The South started the war. The North finished it.

France, Spain, Portugal, and Brazil didn't allow slavery to die out. They abolished it.