Textbook
Paul S. Boyer, et al., eds., The Enduring Vision: A History of the American People, 6th ed. (Boston, MA: Houghton Mifflin Company, 2008), 393.
In the campaign [of 1848], both parties tried to ignore the issue of territorial slavery, but neither succeeded. A faction of the Democratic Party in New York that favored the Wilmot Proviso, called the Barnburners, broke away from the party, linked up with former Liberty party abolitionists, and courted antislavery "Conscience" Whigs to create the Free-Soil party. Declaring their dedication to "Free Trade, Free Labor, Free Speech, and Free Men," the Free-Soilers nominated Martin Van Buren on a platform opposing any extension of slavery.