In the early nineteenth century, many “second sons” of slave-holding families (who would not inherit the family plantations) moved west into the Mexican state of Texas, where land was plentiful and well suited for many of the same cash crops as were grown in other parts of the American South. Although these settlers were at first welcomed by the Mexican government, when the country abolished slavery in 1829, they instigated an independence movement that quickly escalated into a war. In 1836, after the Battle of San Jacinto, Mexico recognized Texas as an independent republic; yet tensions remained between the two nations over the disputed territory between the Nueces River and the Rio Grande, some 150 miles to the south.

When the United States agreed to the annexation of Texas in 1845, it also adopted the Rio Grande as the border, leading to a break in diplomatic relations with Mexico and, eventually, to Democratic President James K. Polk’s request for a war declaration in 1847. Polk asserted that the Mexican army had attacked on American soil; skeptical Whigs, including the freshman congressman from Illinois, Abraham Lincoln, questioned the veracity of Polk’s claim. Lincoln and his political compatriots accused Polk of illegitimately escalating a conflict over disputed territory for the sole purpose of extending slave territory. Indeed, Lincoln presented a series of resolutions on the floor of Congress, challenging Polk to identify the very spot where the alleged Mexican attack had occurred and to prove that it was, in fact, on America soil. The “spot resolutions,” as they became known, showcase Lincoln’s famous wit, but with a degree of acerbity that ultimately proved fatal to Lincoln’s career in the House, as Democrats charged him with being unpatriotic, unsupportive of the Army, and even disloyal.

Lincoln’s senior colleague, Henry Clay, also opposed the war publicly, but since his son fought and died in the battle of Vera Cruz, the Democratic press regularly portrayed Clay as two-faced and his opposition as insincere and politically motivated. In “The Great Speech of Clay,” one political cartoon with this trope, Clay’s anti-war audience (to the right) includes Horace Greeley, editor of the New York Tribune, who compares the position of anti-war Whigs with that of the New England Federalists who organized the Hartford Convention. This trope was taken up by at least one member of Congress in a speech haranguing his fellow legislators for their faithlessness to the war effort they had voted to commence only a short time before.

Not all opposition to the war was politically motivated, however: many Northern religious leaders, some of whom were pacifists on principle and some of whom were ardent anti-slavery advocates, freely denounced the war as an act of imperialism and a blatant attempt to increase the territory available to Southern slaveholders. Interestingly, Ulysses S. Grant’s account of the mindset of the troops on the ground in Texas during the conflict supports the latter interpretation (although it is worth noting that the date of Grant’s memoir is significantly after the fact).