During the mid-1840s, John Calhoun, who was considering a presidential candidacy for 1848, had an interesting idea for cementing a Southern/Western alliance to back him. The way to do this was suggested by Calhoun's lieutenant Duff Green. Green reported Senator Hannegan of Indiana as saying that "the West will be united and will demand funds for the improvement of their harbours, rivers, and the Cumberland road, and the graduation of the prices of public lands, and that if the South will give these to the West, the West will go with the South on the tariff..."
https://books.google.com/books?id=WVRDf1W8NPEC&pg=PA1055
With this in mind, Calhoun underwent a partial reversion to his early days as a nationalist. As Avery Craven explained (
The Coming of the Civil War, pp. 212-13; all the quotes in this post are from that book unless otherwise indicated):
"With this Western temper in mind, in November, 1845, Calhoun attended a convention at Memphis, Tennessee, to promote Western trade and internal improvements. He acted as presiding officer and, on June 26 of the following year, presented to the Senate a report on the Memorial of the Memphis Convention. Both at the meeting and in the report, Calhoun argued that, under the power to regulate commerce, the central government could remove 'obstructions from the western waters' as well as build 'lighthouses, buoys, beacons, and public piers for the increased safety and facility of the commerce' of the Atlantic coast. He discovered, as some one said, that the Mississippi River was 'a great inland sea.' This was strange doctrine to come from the great champion of strict construction. Even the Charleston
Mercury drew back with the terse comment that 'if the federal government may do all that the resolutions of the convention propose, we can see no limit whatever to its power of engaging in internal improvements.' The New York
Evening Express, in the same frame of mind, wondered 'at the liberality of Mr. Calhoun's views.'
"Calhoun was, of course, not interested primarily in removing obstructions from the Mississippi. He hoped to 'remove the only barrier, that remain[ed] between the Union of the South and West.' As he wrote to his son-in-law:
"'The improvement of the navigation of the Mississippi was the great barrier, which kept them asunder and threw the West into the arms of the East. I hope I have forever removed it, by showing that the power is clearly embraced by that of regulating commerce among the states.'
"He followed this action by giving his support for graduation and reduction of the price of public lands, and by hinting that he favored such financial policies as Western men desired. Even Robert Barnwell Rhett was brought into line on these measures, consoling himself that all would be righted when Calhoun became President in 1848."
https://books.google.com/books?id=DEWCKlYiocIC&pg=PA212
https://books.google.com/books?id=DEWCKlYiocIC&pg=PA213
What happened to this idea for a South-West alliance? In large part, it was shattered by the Oregon question and by the Mexican War. The Northwest had viewed Polk's election as a mandate for expansion in both Texas and Oregon. When Polk showed a willingness to compromise on Oregon, they were convinced that this was a betrayal by the South of its part of a supposed bargain. Suspicion of bad faith became open protest when Calhoun took the lead in opposing the "notice to Great Britain resolutions." Hannegan reminded the Senate that "Texas and Oregon were born the same instant, nurtured and cradled in the same cradle--the Baltimore [1844 Democratic] Convention--and they were at the same instant adopted by the democracy throughout the land. There was not a moment's hesitation until Texas was admitted; but the moment she was admitted the peculiar friends of Texas turned and were doing all they could to strangle Oregon." In the House, Wentworth of Illinois went further and bluntly accused the South of using the West to secure Texas and then abandoning it to oppose Oregon.
https://books.google.com/books?id=DEWCKlYiocIC&pg=PA214 An anti-slavery Whig like Joshua Giddings was quick to take advantage of the situation; he had previously voted against terminating the joint occupation of Oregon but explained that the annexation of Texas by the Slave Power had changed everything: "The whole of Oregon" was necessary to restore the "balance of power" and to free the North which was "politically bound, hand and foot, and surrendered to the rule and government of a slaveholding oligarchy." He argued that a war with Britain would be a lesser evil for the "laborers of the free states" than acquiescence to Southern rule.
https://books.google.com/books?id=DEWCKlYiocIC&pg=PA215
Furthermore, the hopes raised by the Memphis Convention were not fulfilled. The Northwest did vote for the Walker Tariff favored by the South, but felt that there was no reciprocity: A river and harbor bill passed in 1846, but southern opposition developed, led by Rhett and his South Carolina friends, and the bill was ultimately vetoed by Polk on constitutional grounds. The West was outraged, and the Chicago
Democrat noted of the House vote that:
"No man in Louisiana voted for it. No one in Mississippi. Only one in Tennessee...Only two of the five Missouri members...No one in South Carolina or Alabama. Only one in North Carolina. Only one in Georgia. So much for the Memphis Convention."
https://books.google.com/books?id=DEWCKlYiocIC&pg=PA217
I think that it is necessary to keep these disputes in mind as the background when one considers Northwestern support for the Wilmot Proviso. I do not say that Northwestern opposition to slavery expansion was not sincere, even though many of these same Northwesterners had ardently supported the annexation of Texas. (Admittedly, there was a distinction in that Texas already had slavery before its annexation, which was not true of the Mexican Cession.) What I am saying is that such opposition took place in a situation where Northwesterners saw such expansion as part of a pattern of Southerners selfishly doing everything they could to further the interests of slavery and ignoring all other interests.
So could Calhoun's idea--the South supports the West on internal improvements (at least with respect to navigation), the West supports a lower tariff--have worked? Ironically, the best prospect for it to have worked would be one that would have displeased Calhoun: Clay being elected in 1844, compromising on Oregon (as Polk did) and (unlike Polk) declining to annex Texas, and instead doing what Gary J. Kornblith has suggested in "Rethinking the Coming of the Civil War: A Counterfactual Exercise",
Journal of American History, Vol. 90, No. 1 (June 2003)
https://web.archive.org/web/2017082...te/assets/documents/02_JAH_2003_kornblith.pdf:
"In all likelihood, Aberdeen and Clay would have joined diplomatic forces in support of Texan sovereignty. In early 1845 the British and French undertook a new initiative to convince Mexico to recognize Texan independence, and Mexican authorities reluctantly agreed. Although the Mexican government would have felt less compelled to comply had Clay rather than Polk been elected, it could not have comfortably ignored the combined pressure of Great Britain, France, and the United States. We may postulate that sooner or later during Clay's presidency Mexico would have recognized Texan independence and entered into international arbitration over boundary issues. Even had the Mexican government continued to refuse official recognition, it would probably have shrunk from open warfare and allowed the Lone Star Republic to consolidate authority and power further."
The expansion issue would thus be at least temporarily ended. Both Northwestern and Southern Democrats would be angry at Clay but would realize that there was little they could do about expansionism immediately. They would have to concentrate on winning back the White House in 1848, and to do this they would have to show the Northwest that the Whigs were not the only people who believed in the internal improvements Northwesterners wanted. Meanwhile, they would argue that with war with both Britain and Mexico avoided, there was less need for revenue, so they would push for tariff reductions. If Clay would veto them, they would then use such a veto as an anti-Whig issue (true, this would hurt the Democrats in Pennsylvania, but you can't please everyone). There are obviously some obstacles to such an alliance, notably that as in OTL some southern Democrats would be less flexible than Calhoun with respect to internal improvements. But perhaps seeing the Whigs control the White House might make them a bit more flexible.
In OTL, of course, relations between the South and Northwest became worse and worse. By 1860 it was the Northwest that was fiercest for the use of force, and it was in the cities of the Northeast that compromise proposals had the most support. There were many factors involved in the gradual transformation of the Northwest's attitudes, including a change in the composition of the population of the Northwest (which had originally been settled mainly by Southerners but later got more and more Northern and foreign migrants). And of course the Kansas-Nebraska issue--which (unlike the Mexican Cession) threatened the expansion of slavery into the very areas Northwesterners wanted to settle--played a major role. But much of the division does have its source in Polk's perceived "betrayal" of Oregon and favoritism toward the South. If only a Whig could be blamed for betraying both Texas and Oregon (with the Democrats sadly acknowledging that there is nothing much that could now be done about it[1]), and if the Democrats could show that they were as sensitive as Whigs to the West's desire for improving the navigation of the Mississippi, Great Lakes, etc., the split between Northern (especially Northwestern) and Southern Democrats might be, if not prevented, at least very considerably delayed. (In OTL this dispute erupted full-scale during the Wilmot Proviso debate and was only papered over for a few years by the Compromise of 1850. Of course even after 1854 the majority of Northwestern Democrats remained loyal to the Democratic Party, but there were enough defections so that the party no longer had a majority in the Northwest.)
[1] In particular, I do not see too much further Southern pushing to annex Texas if the mediation is successful and does not interfere with slavery there. Unlike some people, I am inclined to think that the Tyler administration Southerners who screamed about a British plot to abolish slavery in Texas were sincere--at least Upshur seems to have been: in a private letter he advised his friend Beverley Tucker to get his (Tucker's) slaves out of Texas because slavery probably wouldn't last very long there. As Kornblith notes, "A President Clay would have objected to any British effort to promote abolition in Texas for the same reason he opposed annexation of Texas: his overriding concern was the maintenance of sectional harmony and American political stability." Aberdeen, who was already temporizing on his earlier support for abolition in Texas, would doubtless go along with Clay. By 1848 the specter of the Texas Republic abolishing slavery under British pressure would probably be dead. (See William W. Freehling's
The Road to Disunion" Vol. 1: Secessionists ay Bay, 1776-1854 for an argument that Southern fears of Britain inducing Texas to abolish slavery were not only sincere but by no means totally unjustified.)