The antislavery faction, comprised mostly of Northerners, helped fugitive slaves reach safety in a loose, secret network dubbed “the Underground Railroad,” sometimes called “the Liberty Line.” This enabled runaway slaves to achieve safety in the free states or in Canada. Of course, even in free states runaway slaves would not be safe, as the federal Fugitive Slave Law under the Compromise of 1850 required that they be returned to their owners. Begun in the 1780s by Quakers, the Underground Railroad grew legendary after the 1830s. It's thought that approximately 60,000 slaves gained freedom through this lifeline.

Many hiding out in the Underground Railroad traveled less conspicuously at night, using the North Star for guidance. Isolated farms or towns sympathetic to a slave's plight would effectively conceal them. Harriet Tub-man, an escaped slave, became known as the Moses of the blacks for her work in rescuing slaves and leading them to freedom.

Even under these circumstances, escaping slavery was an arduous task. Vigilant officers in search of rewards often spotted runaway slaves, seizing them as they made their passage north. But even if the slaves didn't always reach safety, their efforts did give validity to the antislavery cause, forcing many to publicly acknowledge the wrongs of slavery. Even the federal Fugitive Slave Laws of 1793 and 1850 became difficult to enforce as Northern judges restricted the rights of many a slave's master. This further enraged the Southern states, galvanizing sentiment toward Civil War.