Underground Railroad (“Farewell, old master, don’t think hard of me / I’m on my way to Canada, where all the slaves are free”). The antislavery activist Sojourner Truth wrote her own version, which began, “I’m on my way to Canada, that cold but happy land / The dire effects of slavery I can no longer stand.”

Throughout his life Foster was careless with money. He handed out manuscript copies of “Oh! Susanna” like spare kittens, and in 1848 he sold what remained of the rights for one hundred dollars to a publisher who would earn an estimated ten thousand dollars from the song. Still, “Oh! Susanna” launched Foster’s career as a songwriter. Over the following decade and a half he turned out such classics as “Old Dog Tray,” “My Old Kentucky Home,” “Massa’s in de Cold Ground,” and “Beautiful Dreamer,” making little money from them and saving none, before he died a drunken pauper’s death in a New York City slum in 1864.

The Halls of Montezuma

On September 14 the United States Army, commanded by Gen. Winfield Scott, raised the American flag over Mexico City, capping a year and a half of sporadic fighting that had begun in a dispute over the Texas border. After defeating the Mexicans at Cerro Gordo in April and occupying nearby Perote and Puebla in May, the Americans had spent three months resting, firming up supply lines, and awaiting reinforcements. In August the revitalized army, a bit more than ten thousand strong, struck out for Mexico City. The capital lay seventy-five miles away over desert and mountain terrain infested with fever and guerrillas. It was defended by almost three times as many troops and a fearsome collection of well-placed artillery.

In England the Duke of Wellington, who had defeated Napoleon three decades earlier, foresaw disaster: “Scott is lost—he cannot capture the city and he cannot fall back upon his base.” Yet in a campaign that saw “four of the hardest foug[h]t battles that the world ever witnessed” (as Lt. Ulysses S. Grant wrote to his fiancée), the Americans obtained their objective at strikingly little cost.

On August 19 and 20 they began to tighten the noose by winning a pair of battles on the city’s outskirts. The Mexicans obtained an armistice on the pretext of seeking peace, but their demands were completely unrealistic, and it soon became clear that they were just stalling. On September 8 the Americans renewed the offensive with their only major misstep of the campaign. They attacked a small group of buildings called Molino del Rey, where the Mexicans were reportedly melting church bells to cast artillery pieces. After incurring almost 800 casualties (116 dead, 665 wounded—a fourth of those engaged), the Americans finally captured the installation. They found no evidence of a foundry—nothing, in fact, but the guns the Mexican troops had used to defend themselves.

With that misbegotten battle concluded, the Americans began

planning the final push to the city’s gates. Over those last few days, Scott’s most valuable scout and engineer, Robert E. Lee, stayed awake for more than sixty hours straight while surveying terrain, carrying messages, and building artillery positions, before he finally fainted in his saddle from exhaustion. On September 12 the Americans began shelling Chapultepec, the last remaining fortification guarding Mexico City’s gates. Early the next morning an infantry attack captured the stronghold in another bloody struggle, the final major battle of the war. With Chapultepec’s fall, the remaining Mexican troops evacuated the city and municipal officials surrendered to the invaders.

In a brilliantly conceived and executed campaign, Scott had captured a well-fortified enemy capital with a greatly outnumbered army cut off from supplies and reinforcements. Wellington was as effusive in praise of Scott as he had earlier been dismissive: “His campaign is unsurpassed in military annals. He is the greatest living soldier.”

Unfortunately the war was not a board game that ended with the capture of the opponent’s flag. Peace negotiations went slowly, in part because neither side was sure who was in charge. Mexico’s government was in constant turmoil, and America’s chief emissary, Nicholas Trist, was recalled in November but wavered for weeks before deciding to ignore the order. While diplomats dithered, American forces dealt with snipers and rebels within Mexico City, beat off a siege of their garrison at Puebla, talked warily with separatists in Baja California and the Yucatán, made plans to occupy the Isthmus of Tehuantepec, skirmished with guerrillas who harassed their supply lines, occupied more towns and seaports, and quarreled fiercely among themselves over who deserved credit for the victory. Finally, on February 2, 1848, a peace treaty was agreed on. Formal ratifications were not exchanged until late May, and the last American troops did not leave Mexico until August, nearly a year after the capital had fallen.