Woodruff recorded in his journal that Smith told Mormon missionaries "to 'confine' their activities 'to the free states' and not go into any of the 'Slave States'." Bringhurst feels this was due to southern antipathy to Mormonism as "a northern-based movement" with "distinctive doctrines and teachings" peculiar to a Yankee world-view that the southerners could not embrace.
[Source: Bringhurst, Saints & Slaves (pp. 60 and 77 n. 48), in LDS (or related) Documents on Walker Lewis, the Lowell, Mass. Branch of the Mormon Church and its missionaries and members, and the Priesthood Ban against Blacks, Compiled by Connell O'Donovan http://people.ucsc.edu/~odonovan/Mormon_Chronology.html]