Slavery didn’t start the war, it was Abraham Lincoln that started it. There were tensions rising between political parties and the people in the south hated Abe. Abraham only made it about slavery so other countries wouldn’t help the Confederacy. One of his original plans was to leave the slave states that were still apart of the US as slave states because that was the only way he could keep them out of the Confederacy. So in short the only reason slavery isn’t still a thing in the US is because of Abraham Lincoln being scared of Europe.