Joseph advocates non-interference with slavery.
Joseph Smith, Jr., Letter to Oliver Cowdery, Messenger and Advocate vol. 2, no. 7 (April 1836): 1-2
Trace the history of the world from this notable event down to this day, and you will find the fulfillment of this singular prophecy. What could have been the design of the Almighty in this wonderful occurrence is not for me to say; but I can say, that the curse is not yet taken off from the sons of Canaan, neither will be until it is effected by as great power as caused it to come; and the people who interfere the least with the purposes of God in this matter, will come under the least condemnation before him.