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chapter฀three The Old Army’s Vindication The Mexican War ฀฀ One historian has called the Mexican War a “rehearsal for conflict”—a sort-of dry run for the larger conflict that occurred thirteen years later.1 Many future West Point generals learned their trade in the field during the Mexican War, whose lessons and legacies would prove both problematic and indispensable for the later fratricidal conflict. Many of the earlier war’s distinguishing characteristics foretold to some extent the later clash of arms: conflicts between professionals and citizen-soldiers, civil-military tensions at the highest levels of war making, domestic political disagreements with battlefield implications, and a contentious debate over slavery ’s future in the republic. Nevertheless, the Mexican War’s actual combatants possessed no such foresight, and our own knowledge of the Civil War can be as much hindrance as blessing in understanding the Mexican War on its own terms. One important underlying cause of the Civil War—the political dispute over the fate of slavery in territory acquired after the Mexican War—required a decisive American victory in Mexico. Unfortunately, any study that looks back on the Mexican War from the later sectional conflict can fall prey to glibly assuming the existence of that decisive victory . Much of the war’s far-from-preordained results stemmed from the deliberate creation of a reasonably competent professional military establishment in the United States after the end of the War of 1812. Furthermore , the outcome of individual battles and campaigns frequently hung in the balance, depending on the vagaries of individual command decisions and the capricious fortunes of war.2 Nevertheless, American military professionals interpreted the war in a straightforward fashion. Indeed, the war vindicated their faith in professional military expertise, and the stunning success of American arms can- 55  the฀old฀army’s฀vindication not gainsay that belief. After two years of active campaigning, the United States in effect conquered 529,017 square miles of territory, including the valuable and future state of California. In terms of both blood and treasure , approximately 12,876 American soldiers lost their lives while the monetary costs broke down to forty-eight cents an acre.3 These costs were far from trivial, but they remain astonishingly low. Whatever its morality or lack thereof, when seen in purely military terms, we must declare the Mexican War a glorious triumph for American arms. In retrospect, that triumph was all the more impressive in light of its less than entirely expected nature. Both Mexican and British observers had a reasonably fair understanding of the deep flaws in the vaunted militia system, an understanding far more plausible than most contemporary Americans’ ideologically jaundiced view of the subject. Mexican scorn for the small regular army, which stood 3,300 men short of its authorized strength of 8,613, had much truth to it. The laborious reforms of the War of 1812 generals and their pupils at West Point had not yet met any test in battle. The Mexicans also knew of the decidedly mixed record of American arms during the previous war with England. The Times of London in April 1845 declared that “neither of the belligerents possesses an army at all proportioned to the vast extent of the operations necessary to accomplish any practical result.” Poinsett himself expressed great admiration for the irregular Mexican cavalry while serving as the American minister to Mexico, while the British, Spanish, and Prussian ministers at Washington would later predict failure for Winfield Scott’s Vera Cruz campaign.4 Moving beyond questions of tactical competence, Mexico also seemed to have serious advantages. Mexico had many similarities to the rebellious colonies of the American Revolution and the United States during the War of 1812—it possessed a vast territory with primitive transportation infrastructure, great strategic depth, a population at least somewhat hostile to the invader, and all the advantages of defensive warfare. The United States had won both of those earlier wars despite much bungling and misdirection with military forces that possessed as many flaws as the problem-ridden Mexican army. Rugged and unforgiving terrain marked northern Mexico, along with a climate difficult for any army and its accompanying logistics. The region also afforded the Mexicans a good deal of strategic depth, or, to use the words of Charles Elliot, British minister in Texas, “I believe that it would require very little skill and scarcely any exposure of the defending force to draw the invading columns well forward beyond all means of support [3...

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