IRREPRESSIBLE CONFLICT, a term originating with William H. Seward in an 1858 speech in which he predicted the collision of the socioeconomic institutions of the North and the South. This confrontation, Seward maintained, would determine whether the nation would be dominated by a system of free labor or slave labor. Abraham Lincoln posited the same idea in his 1858 "House Divided" speech. At the time, the use of the phrase did not include the assumption that the "irrepressible conflict" would necessarily find expression in violence or armed conflict.
Cole, Arthur C. The Irrepressible Conflict: 1850–1865. New York: Macmillan, 1934.