The Constitution for the United States affirmed that slavery was lawful and that it would taken a Constitutional Smendment to abolish it.
Om 1860 there were 34 states and to ratify an amendment to abolish slavery would have required the approval of 26 states. Because only 23 states would have supported such a proposed amendment. Even of if the amendment had been ratified the requisite number of states Limcoln found it necessary violate the Constitution in order to save the Union.