UNIVERSITY PARK, Pa. -- "I do not think there was ever a more wicked war than that waged by the United States on Mexico," wrote Ulysses S. Grant in 1879. Grant knew something about war, having served as a lieutenant in the conflict with Mexico and as the North's most victorious general in the Civil War. Although he is not a key figure in Amy Greenberg's new book, "A Wicked War: Polk, Clay, Lincoln, and the 1846 U.S. Invasion of Mexico," (Alfred A. Knopf) his view aptly illustrates her main point: the U.S.-Mexican War was opposed by a large segment of the American people, including many of those who actually fought in it.

The war gave rise to the first truly national anti-war movement in the United States, according to Greenberg, Edwin Erle Sparks Professor of History and Women's Studies at Penn State. It far surpassed opposition to the War of 1812, largely confined to New England. Both the war with Mexico and the anti-war movement of the 1840s, Greenberg writes, helped to shape national values and "to this day affects how the United States acts in the world."

Greenberg depicts the war through the lives of five men: President James K. Polk; Senator Henry Clay of Kentucky; Abraham Lincoln, elected to Congress from Illinois in 1846; Lincoln's political rival, James J. Hardin, who was among the first to volunteer for military service and raise troops; and diplomat Nicholas Trist, who went to Mexico City to deliver an ultimatum of surrender but saw first hand the folly of the war and ended up negotiating a far less severe peace treaty with Mexico than Polk desired.

Ironically, it was Clay -- one of the "war hawks" of 1812 -- who emerged as an eloquent voice against war with Mexico. The issue was the annexation of the Republic of Texas. Clay, the Whig Party's presidential candidate in 1844, correctly argued that U.S. annexation of Texas would automatically mean war with Mexico, which regarded Texas as still part of its domain. In Clay's view, Texas was not worth a war.

To Democratic Party candidate James Polk, it was. Polk regarded annexation and war as a means to seize additional Mexican territory -- perhaps even all of Mexico -- thus fulfilling what he regard as his nation's "manifest destiny" to expand to the Pacific shore.

"Historians have previously concentrated on the military side of the war," Greenberg said. "I wanted readers to become more aware of other issues, such as slavery, the reaction of civilians to war-related atrocities, and the high cost of the war in terms of its casualties -- it had the highest mortality rate of any American war. These were the issues that fueled the anti-war movement."

Clay and Lincoln's anti-war sentiments have been known, but are largely glossed over by historians more concerned with Clay's forceful advocacy of America as a great economic engine and Lincoln's presidency. Greenberg, however, focuses on those sentiments. Clay saw war as extending slavery into new territory, and undermining his platform of industrialization and internal improvements. Lincoln, a fellow Whig, was inspired by that platform and repulsed by the violence that he witnessed during his service as a captain in the brief but bloody Black Hawk War.

Probing even more deeply into unexplored historical territory, Greenberg also brings to light the important roles played by the wives and families of the five men she highlights. President Polk's land-grabbing ambitions, for example, were aided and abetted by his wife, Sara Polk, a woman who did not hesitate to express her firm convictions about public issues -- a novelty in American politics at the time. "Far from being threatened by her strong opinions and political acumen," Greenberg writes, "James embraced his wife's capabilities." Previous historians, according to Greenberg, have ignored the influential role Sara Polk played in presidential decision-making.

"Dolly Madison is often thought of as the first truly influential first lady," Greenberg said. "It's true in the sense that she used her important social role to advance her husband and his party, but Sara Polk was the first to be part of the actual political decision-making process. The evidence suggests that James Polk's policy-making included input from Sara."

Greenberg has aimed her book at a general audience rather than academicias.

"I wanted more people to realize that dissent against war is deeply rooted in American history," she explained. "The U.S.-Mexican War experience legitimized dissent and helped us to question the difference between wars for aggrandizement and wars for national principle."