California and New Mexico became the strategic points of the slavery struggle at the close of the war.  To open both to the immigration of slave-labor was thenceforth the grand design of the South.  Over Oregon occurred a fierce preliminary trial of strength between the sections.  The South was thrown in the contest, and the anti-slavery principle of the Ordinance of 1787 applied to the Territory.  Calhoun, who was apparently of the mind that as Oregon went so would go California and New Mexico, was violently agitated by this reverse.  “The great strife between the North and the South is ended,” he passionately declared.  Immediately the charge was made and widely circulated through the slave States that the stronger was oppressing the weaker section, wresting from it its just share in the common fruits of common victories.  For had not California and New Mexico been won by the bravery and blood of the South as of the North, and how then was the North to deprive the South of its joint ownership of them without destroying the federal equality of the two halves of the Union?  What was it but to subvert the Union existing among the States?

Disunion sentiment was thenceforth ladled out to the slave States in increasing quantities.  The turning of the long lane in the domination of the slave-power was visibly near.  With Garrison at one end and Calhoun at the other the work of dissolution advanced apace.  The latter announced, in 1848, that the separation of the two sections was complete.  Ten years before, Garrison had made proclamation that the Union, though not in form, was, nevertheless, in fact dissolved.  And possibly they were right.  The line of cleavage had at the date of Calhoun’s announcement passed entirely through the grand strata of national life, industrial, moral, political, and religious.  There remained indeed but a single bond of connection between the slave-holding and the non-slave-holding States, viz., fealty to party.  But in 1848 not even this slender link was intact.

The anti-slavery uprising was a fast growing factor in the politics of the free States.  This was evinced by the aggressiveness of anti-slavery legislation, the repeal of slave sojournment laws, the enactment of personal liberty laws, the increasing preference manifested by Whig and by Democratic electors for anti-slavery Whig, and anti-slavery Democratic leaders.  Seward and Chase, and Hale and Hamlin, Thaddeus Stevens and Joshua R. Giddings, were all in Congress in 1849.  A revolution was working in the North; a revolution was working in the South.  New and bolder spirits were rising to leadership in both sections.  On the Southern stage were Jefferson Davis, Barnwell Rhett, David Atchison, Howell Cobb, Robert Toombs, and James M. Mason.  The outlook was portentous, tempestuous.