What was the Underground Railroad and how did it work?

The Underground Railroad was a network of secret routes and safe houses established in the United States during the early to mid-19th century, and used by African-American slaves to escape into free states and Canada with the aid of abolitionists and allies who were sympathetic to their cause. It worked by having African American Slaves move from safe house to safe house, like stops on a railroad. These people would eventually make their way north to seek freedom.