“We’re all very good at leading our daily lives, our private lives, and setting aside the things that we don’t want to know about in the broader world,” Andrew Delbanco says on this podcast. “Now and again, something happens that makes it almost impossible to do that.”

One of those things happened in 1850, when Congress passed the Fugitive Slave Act. In his new book, “The War Before the War,” Delbanco argues that disputes over the fates of fugitive slaves did much to accelerate the divisions that led to the Civil War.

“The fugitive slave law was an important force in bringing the public and the personal together for more and more Americans, and thereby woke them up to the fact that this was an existential moral problem,” Delbanco says. “How could you have a democratic republic based on the principle of liberty and equality in which millions of human beings were enslaved, some of whom were courageous enough to actually escape and tell you about it? It became more difficult to keep one’s head in the sand.”