Before the Fugitive Slave Law of 1850, runaway slaves only needed to escape to the free northern states to begin new lives. But once they reached New York City, Cleveland, Philadelphia, Hartford, and elsewhere, they found that running away was only the beginning of their new struggle. Most fugitives had few job skills, could not read or write, and found little work open to them. Blacks were turned away from dining in restaurants and denied access to schools and churches. Public transportation was segregated, and hotels closed their doors to blacks. Although they were free to do as they pleased, that also meant they were free to starve.

Many ex-slaves thought that they would receive better treatment in Canada, and even before the Fugitive Slave Act, thousands of southern blacks pressed on past America's northern border. After the Fugitive Slave Law...