By the summer of 1847, according to Greenberg, even journalists employed by pro-war newspapers “found themselves forced to report on and condemn American atrocities that left them questioning their assumptions about American morality.”
Although most voters in Western and Southern states supported the war, as the months went by and no end appeared in sight, antiwar sentiment increased even though American arms experienced nothing but victory. The slavery issue compounded the controversy. Much antiwar opinion was fueled by the suspicion that the principal purpose of the conflict was to acquire more territory for slavery. As early as August 1846 a Pennsylvania congressman named David Wilmot introduced an amendment to an appropriations bill for the war stating that “as an express and fundamental condition to the acquisition of any territory from the Republic of Mexico…neither slavery nor involuntary servitude shall ever exist in any part of said territory.”3
This famous “Wilmot Proviso” framed the national debate over slavery for the next fifteen years. Nearly all Northern Democrats joined all Northern Whigs in the majority that passed the amendment, while Southern Democrats and Southern Whigs voted against it. In the Senate, greater Southern strength defeated the proviso. This outcome, which was repeated several times in the next two Congresses, marked an ominous wrenching of the party division, between Whigs and Democrats, into a sectional division between free and slave states that foreshadowed the political breakdown that led to secession and war in 1861.
As the war dragged on despite American conquest of a huge swath of Mexico, Polk wanted to negotiate peace and complete the accomplishment of his territorial goals before he lost control of events. Enter Nicholas Trist, the fourth of Greenberg’s characters and the real hero of her narrative. Probably not one in a hundred Americans today could identify Trist, yet he was prominent in his time. A protégé of the elderly Thomas Jefferson, who supervised his legal education and made him his private secretary, Trist also married Jefferson’s granddaughter. Later he served as Andrew Jackson’s personal secretary for a time, and in 1845 Jackson persuaded Polk to appoint Trist as chief clerk of the State Department—the equivalent of assistant secretary of state.
Fluent in Spanish, a Democrat and expansionist, Trist seemed the ideal person to negotiate a peace with Mexico that would force its government to yield half its country to the United States. Polk appointed him as a special envoy to accompany General Winfield Scott’s army, which was closing in on Mexico City. Trist was authorized to offer Mexico up to $20 million in return for the Rio Grande boundary of Texas plus New Mexico and California (embracing the present-day states of California, Nevada, and Utah, most of Arizona and New Mexico, and part of Colorado). If Mexico would also throw in Baja California, Trist could pay up to $30 million.
During Trist’s sojourn in Mexico, a number of things happened that set up a dramatic confrontation between the envoy and the president who sent him there. Scott’s army captured Mexico City in September 1847 and drove President Santa Anna and his army away to Guadalupe Hidalgo, where Santa Anna refused to capitulate or negotiate despite the hopelessness of his cause. American military success whetted the appetite of some Manifest Destiny expansionists for more of Mexico than Polk had initially contemplated, perhaps even “all Mexico.”
Polk also began to think that he should demand more territory. But Trist found himself questioning the morality and justice of American policy. His dispatches indicated a growing softness toward Mexico and an unwillingness to go beyond the original territorial goals he had been instructed to achieve. In October 1847 Polk decided to recall Trist and send a new envoy to extract harsher terms. Trist ignored the recall order, at the risk of his career, and in February 1848 he finally negotiated the Treaty of Guadalupe Hidalgo with Santa Anna’s successor, which carried out Polk’s initial territorial goals (minus Baja California).
The arrival of this treaty in Washington presented Polk with a dilemma. He was furious with Trist and tempted to repudiate his treaty in order to force greater concessions from Mexico. But since the autumn of 1847 a growing antiwar movement had begun to threaten to crush Polk between the millstones of Democrats’ “all Mexico” clamor and Whig pressures for “no Mexico.” In November 1847 Henry Clay, still mourning the death of his son, broke his silence on the Mexican War with a powerful antiwar speech in Lexington, Kentucky, that received national publicity.
Among others, it solemnly affected Abraham Lincoln, Greenberg’s fifth main character, who happened to be in Lexington visiting his in-laws while on his way to Washington to take the congressional seat to which he had been elected in 1846. Lincoln heard Clay denounce an “unnecessary” war of “offensive aggression” that had produced “sacrifice of human life…waste of human treasure…mangled bodies…death, and…desolation” in a conflict “actuated by a spirit of rapacity, and an inordinate desire for territorial aggrandizement.” Clay also endorsed the Wilmot Proviso and insisted that the United States must not “acquire any foreign territory whatever, for the purpose of introducing slavery into it.”
Clay’s speech inspired many antiwar meetings around the country and emboldened Whigs to speak out more vigorously against Mr. Polk’s War in the congressional session that began in December 1847. One of those Whigs was Abraham Lincoln. Greenberg maintains that before hearing Clay’s speech, Lincoln had said little about the Mexican War or about slavery, and that Clay galvanized him to take up the antiwar and antislavery cause for the first time. Whether she is right is debatable, but it is quite true that the freshman congressman achieved national exposure with his “spot resolutions” and speeches in the House advocating these resolutions in December 1847 and January 1848. The resolutions demanded from Polk a description of the exact “spot” where Mexican soldiers shed American blood to start the war, suggesting instead that American soldiers shed Mexican blood on Mexican soil.
The political turmoil surrounding the debates about responsibility for the war forced Polk to conclude that he should get the controversy behind him by submitting Trist’s treaty to the Senate for ratification rather than try to negotiate a new treaty. In the Senate, several Democrats who wanted more Mexican territory and several Whigs who wanted none voted against ratification, but enough senators of both parties voted in favor to pass the treaty with four votes to spare. “Had Nicholas Trist not concluded that justice required him to disobey his president and negotiate a lenient peace treaty with Mexico,” writes Greenberg, “no Treaty of Guadalupe Hidalgo would have emerged in 1848.” Polk fired Trist from his job in the State Department and even withheld his pay for the time he spent in Mexico. Clay also forfeited any chance for another presidential run in 1848 by jettisoning his political base in the South and West, where the war and conquest remained popular. And the Whigs lost Lincoln’s congressional district in 1848, in part because of the unpopularity there of Lincoln’s antiwar speeches.
Greenberg’s narrative is the best account we have of the politics of Mr. Polk’s War. Yet the reader should be wary of her penchant for sweeping declarations that sometimes seem to go beyond the evidence. Was Sarah Polk really “one of the most powerful First Ladies in history”? Is it actually true that if it had not been for Henry Clay’s Lexington speech against the war, “Lincoln might not have opposed the war at all”? Perhaps one can accept that Nicholas Trist was “the only man to single-handedly bring an American war to a close,” but can we agree that John Hardin’s death at Buena Vista “removed a key obstacle from Lincoln’s rise to power”? And perhaps the assertion that the Mexican War “decisively broke with the past, shaped the future, and to this day affects how the United States acts in the world” claims too much.
These statements concern matters of interpretation and emphasis that, by their nature, cannot be proven right or wrong, although for many readers this American political conflict over the legitimacy of a bloody war recalls many of the debates over American military intervention since the Vietnam War of the 1960s. But Greenberg’s assertion that “the US-Mexican War had the highest casualty rate of any American war” is quite definitely wrong. The long-accepted figure of 620,000 Civil War soldier deaths, 21 percent of the three million soldiers and sailors who fought in that war, exceeds the 17 percent of American soldiers who died in the Mexican War. The number of Mexican deaths is unknown. More new research by the demographic historian J. David Hacker finds that the total number of Civil War dead was probably about 750,000, or approximately 25 percent.4
It is natural for a historian to claim preeminent significance for her or his subject, and Greenberg has certainly made a strong case for the importance of hers. She also places it in a setting that helps explain why another war that almost destroyed the United States came in 1861, in considerable part the consequence of what happened from 1846 to 1848. If one can read only a single book about the Mexican-American War, this is the one to read.
3 Congressional Globe, 29th Congress, 1st Session (August 12, 1846), p. 1217. ↩
4 J. David Hacker, “A Census-Based Count of the Civil War Dead,” Civil War History, Vol. 57, No. 4 (December 2011). ↩