 Complete the following phrase:  In 1842, Barnes was assigned to Fort Jesup, Louisiana, where he remained until 1846 when with the beginning of the MexicanAmerican War, he joined the 2nd U.S. Dragoons en route to Corpus Christi to join the army being mobilized for the invasion of Mexico from the north. He served with the cavalry column of Major General Zachary Taylors army during its advance to Monterey. Later transferred to Lieutet General Winfield Scotts forces before Veracruz, he served with Major General William J. Worths division during the siege and capture of that city. During the advance upon Mexico City, he was chief surgeon of the cavalry brigade and participated in the battles of Cerro Gordo, Contreras, Churubusco, and 