CONSCIENCE WHIGS. A New England–based, Massachusetts-centered faction of the Whig party, the Conscience Whigs opposed the annexation of Texas and the Mexican War because they feared the extension of slavery to new territories would endanger the republic. In Massachusetts, young, politically ambitious Conscience Whigs defined themselves in opposition to Old Line or Cotton Whigs, who wished to downplay the slavery issue in order to preserve both sectional harmony and the lucrative cotton trade with the southern states. Beginning in 1846 bitter debates over the Wilmot Proviso gradually split the national Whig party and divided northern Whig state parties. Conscience Whigs consistently attacked slavery as immoral and argued that antislavery principles were more important than party loyalty. By the summer of 1848 numerous Conscience Whigs, including Charles Francis Adams and Charles Sumner of Massachusetts, had bolted their old party to help form the national Free Soil Party. Cotton Whigs embraced the Compromise of 1850 and declared the slavery issue dead, but former Conscience Whigs continued to charge that New England's Whig businessmen supported the economic interests of southern slaveholders. Over Cotton Whig protests, in spring 1851 the Massachusetts legislature sent Sumner to the United States Senate, where he subsequently helped lead Free Soil, and after 1854, Republican Party antislavery efforts.
Brauer, Kinley J. Cotton versus Conscience: Massachusetts Whig Politics and Southwestern Expansion, 1843–1848. Lexington: University of Kentucky Press, 1967.