John M. Blum, et al. eds., The National Experience: A History of the United States (New York: Harcourt, Brace & World, Inc., 1963), 283.
In the Northern strongholds of anitslavey sentiment the new law simply could not be enforced; during the 1850s abolitionists executed a series of dramatic rescues of fugitives and sent them on to Canada and freedom. Moreover, various Northern states passed personal liberty laws which nullified the fugitive slave act or at least interfered with its enforcement. This was an assertation of state rights and a form of nullificaton that Southerners scarcely appreciated.