The last Democratic president, James K. Polk, annexed more land to the United States than any administration before or since. Then he opted not to take a second term and the Whigs, who lacked the Democrats gung-ho enthusiasm for expansion by force occupied the White House for four years. The election of 1852 brought Franklin Pierce into the White House and the Democracy eager for still more expansion. Affirming the oath to office in March 4, 1853, the only president to do so rather than swear to it, Pierce turned from Chief Justice Roger Taney and delivered his inaugural address from memory. (Past presidents read their remarks.)
Looking back at the previous four years, Pierce said:
One of the most impressive evidences of that wisdom is to be found in the fact that the actual working of our system has dispelled a degree of solicitude which at the outset disturbed bold hearts and far-reaching intellects. The apprehension of dangers from extended territory, multiplied States, accumulated wealth, and augmented population has proved to be unfounded. The stars upon your banner have become nearly threefold their original number; your densely populated possessions skirt the shores of the two great oceans; and yet this vast increase of people and territory has not only shown itself compatible with the harmonious action of the States and Federal Government in their respective constitutional spheres, but has afforded an additional guaranty of the strength and integrity of both.
In other words, one ought to ignore the fire-eaters preaching secession, the narrow passage of the Compromise measures, the fugitive slave rescues, and all the rest. He had good reason to do so. However many copies of Uncle Tom’s Cabin sold, the fire-eaters secession conspiracy fell before the forces of Southern Unionism. However small the coalition for compromise and Union, it had passed laws that both sections clearly found they could live with. After a first blush of resistance, fugitive slave rescues declined considerably and more fugitives went back into slavery. Expansion might have tested the Union, but the Union endured.
With Union clearly strong enough for expansion, why not another round?
With an experience thus suggestive and cheering, the policy of my Administration will not be controlled by any timid forebodings of evil from expansion. Indeed, it is not to be disguised that our attitude as a nation and our position on the globe render the acquisition of certain possessions not within our jurisdiction eminently important for our protection, if not in the future essential for the preservation of the rights of commerce and the peace of the world.
With an inaugural address like that, Mexico ought to up its defense spending. People of any era might recognize the rhetoric of national security. Nobody launches wars of aggression, only wars of preemptive defense. Much of the Mexican borderlands, like the newly American Southwest, had few population centers that nineteenth century Americans saw fit to respect. Lines on maps might split such empty lands, but the resources of modern nation-states did not police them and sudden revisions by forces on the ground might make their adjustment a fait accompli. Having taken the land for America, would America really demand that a successful filibuster (from the Spanish filibustero for freebooter or pirate) give that land back? Or take the land into the national possession and then cede it back?
America had not done so when the Texans relieved Mexico of some of its territory. Washington supported a similar scheme in California before the war. However easily Polk sold northwestern dreams of expansion short by agreeing on less than the maximum possible claim, pursuing that claim to the point of war with the United Kingdom presented serious risks that beating up Mexico again did not. But the expansionists in Pierce’s exceptionally Southern cabinet and administration had more in mind than the Halls of Montezuma.
Only ninety miles from the naval base on Key West sat one of the few places in the Western Hemisphere, outside of the United States, where slavery still endured. Southerners intent on breaking the 1808 law against the international slave trade often picked up their human cargo in Spanish Cuba. Why not make it, and its half a million slaves, into a new slave state to restore parity in the Senate and further secure the peculiar institution? With slavery already deeply entrenched, Cuba could hardly come in as anything but a slave state, a surety the South could not expect from additional slices of Mexico.