When the
Mexican–American War began shortly afterwards, Polk appointed Pillow brigadier general in the
United States Volunteers, largely to keep an eye on
Zachary Taylor and
Winfield Scott, both political rivals of Polk's. In Mexico, Pillow's superiors, many of them
West Point graduates trained as career soldiers, were unimpressed by the minimal training and experience he had despite his high rank, as a
citizen soldier. Assigned to
Robert Patterson's encampment in Lomita, where he commanded the Second Brigade of the Second Division of Tennessee volunteers, one of his first orders canceled daytime guard duty, a popular move with the troops but a potential major security lapse. He also proposed a reorganization of the troops so divisive that Taylor had to personally resolve tensions. In another move that was associated with him for years afterwards, after ordering his troops to dig a ditch around their encampment, had them put the earth on the wrong side of the ditch, making it useless for defensive purposes.
William B. Campbell, a
colonel in the First Tennessee and later governor of Tennessee, said Pillow's was "one of the smallest capacity elevated to so high a command." Taylor, who described Pillow as having "much to learn" about military matters, left him and his troops behind when he later marched on
Monterrey early in 1847. They saw some minor skirmishes during the
Siege of Veracruz. Pillow made another widely noted misstep one night early in the battle when he ordered half of a company of Pennsylvania volunteers to stand guard on one side of a road while the others slept across from them, a formation that would likely have resulted in heavy casualties had the unit been attacked, leading even privates to hold his generalship in low esteem. At the
Battle of Cerro Gordo, Pillow disregarded orders and chose a more direct route up one of the ridges where the Mexicans under
Antonio López de Santa Anna were positioned. His troops had less cover and had to ascend in single file. The Mexicans opened fire upon seeing them, forcing Pillow to attack the wrong position and ruining Scott's plan to have Pillow's troops serve as a diversionary force for the main U.S. attack. Attempting to get some clarification on how to regroup during the ensuing chaotic retreat,
George McClellan found Pillow, his commander, hiding behind a bush in the rear when an errant canister wounded Pillow's arm, forcing him to retreat even further for medical attention, where he berated his subordinates for their failure to properly support him. Pillow sent McClellan to ask Scott for reinforcements, which were unavailable. When he returned, the Mexicans on the ridges had surrendered as Santa Anna had abandoned them in his retreat. When Pillow returned to Tennessee to heal his arm afterwards, he was harshly criticized by others who had fought under him at Cerro Gordo. He published his own account of the battle, reflecting favorably on him. Pillow was promoted to
major general shortly afterwards, Pillow refused Scott's request that Pillow revise his exaggerated battle reports in which he took credit for the American victories at Contreras and
Churubusco. Then, a letter written by Pillow under the
pseudonym "
Leonidas", published in the
New Orleans Delta in September 1847, wrongfully credited Pillow with the victories at Contreras, including the plan of battle and command of all the forces engaged, and Churubusco. When Pillow's intrigue was exposed, he was arrested by Scott and held for
court-martial for insubordination and violating regulations, along with Colonel James Duncan and Brigadier General
William J. Worth. Pillow wrote to President Polk about Scott's involvement in a bribery scheme proposed by Mexican leader Santa Anna for his help in ending the war without further bloodshed. Polk relieved Scott of command by a letter of February 18, 1848. Polk reduced the proceedings against Pillow, Duncan and Worth from a court martial to a court of inquiry which had no criminal implications and added that Pillow could question Scott about the bribery scheme. Polk and Secretary of War
William L. Marcy chose the three members of the court for their hostility to Scott. of Pillow's name Proceedings began in March 1848 in Mexico City. Major Archibald W. Burns, a paymaster and Pillow protege, claimed authorship of the "Leonidas" letter, at Pillow's behest. When the court of inquiry took as much testimony as they could in Mexico City it reconvened in
Frederick, Maryland. Scott left Mexico City the next day. Scott dropped the charges against Worth and Duncan and Pillow was exonerated when the court announced their findings on July 1, 1848. Scott resumed his duties as general-in-chief of the army early that month. While the affair had cost Pillow politically, it benefited Polk by ending Scott's presidential aspirations. Pillow was discharged from the United States Volunteers in July. Pillow assisted
Roswell S. Ripley in writing
The war with Mexico. On the other hand, Pillow's friend and patron, President Polk, stated after the court of inquiry was closed: "General Pillow is a gallant and highly meritorious officer, and has been greatly persecuted by General Scott, for no other reason than that he is a Democrat in his politics and was supposed to be my personal and political friend." Pillow
attempted to win the vice presidential nomination, but was not taken seriously, and it went to
William R. King. He intended to be a candidate for
vice president in
1856. Instead, he supported his brother-in-law
Aaron V. Brown, who lost that nomination to
John C. Breckinridge. With sentiment in the South increasingly in favor of secession, Pillow was one of the region's few supporters of
James Buchanan in
1856. However, Buchanan did not see fit to reward Pillow with a position in his administration following his victory. The following year, Pillow tried unsuccessfully to secure the Democratic nomination for a seat in the
United States Senate from Tennessee. Pillow supported the candidacy of
Stephen A. Douglas in the
presidential election of 1860, despite being publicly critical of the Democratic nominee. With the election of
Abraham Lincoln as president, Pillow ultimately came to support
secession as the will of the majority in Tennessee, although he remained personally opposed. Pillow's political failures were in contrast to his continuing business success. In addition to his law practice and management of the family farm, Pillow engaged in highly profitable land speculation. By 1860, he was one of the largest landholders in the South and possibly the wealthiest man in Tennessee. ==American Civil War==