In U.S. history, unsuccessful last-minute effort to avert the Civil War. It was proposed in Congress as a constitutional amendment in Dec., 1860, by Sen. John J. Crittenden of Kentucky with support from the National Union party. Basically, it accepted the boundary between free and slave states that had been set by the Missouri Compromise (1820–21), extended the line to California, and assured the continuation of slavery where it already existed. In addition, it advocated slavery in the District of Columbia, upheld the fugitive slave law (1850) with minor modifications, and called for vigorous suppression of the African slave trade. At a peace conference called by the Virginia legislature in 1861, the compromise gained support from four border state delegations. Nevertheless, it failed in the House of Representatives in Jan., 1861, by a vote of 113 to 80 and in the Senate in March by a vote of 20 to 19. Its defeat made clear the inevitability of the Civil War.