What U.S. political party became virtually defunct as a result of Civil War issues?

The Whig party fell apart because of the internal tension over the expansion of slavery to territories in the U.S. With deep fissures in the party on this question, the anti-slavery faction prevented the nomination for a full term its own incumbent, President Fillmore, in the 1852 presidential election. Instead, the party nominated General Scott. Most Whig Party leaders eventually quit politics (as Abraham Lincoln did temporarily) or changed parties. The northern voter base mostly gravitated to the new Republican Party. In the South, most joined the modest Know Nothing Party, which unsuccessfully ran Fillmore in the 1856 presidential election, by which time the Whig Party had become virtually defunct.

However, during Civil War Reconstruction, Whig ideology ( the rule of law and protection for minority economic interests) as a policy orientation persisted and played a major role in shaping the modernizing policies of many state governments in the United States.