In January, 1846, he was ordered to occupy positions on or near the left bank of the Rio Grande del Norte.  This order and its execution have been held by some writers to constitute an act of war, but war was not formally declared by the United States till May 11th.  Taylor, with a small force, had several slight encounters with Mexican troops, after which he won the battle of Palo Alto (May 8, 1846), near the southern extremity of Texas; and that of Resaca de la Palma (May 9th), also in Texas, four miles north of Matamoros, Mexico.  He took possession of Matamoros May 18th.  With six thousand men, against about ten thousand Mexicans under Ampudia, Taylor captured Monterey, Mexico (September 24th), and at Buena Vista, February 22-23, 1847, with five thousand troops, he defeated fifteen thousand Mexicans under Santa Anna, then President of Mexico and commander of her army.

The war was now transferred to the district between Vera Cruz and the City of Mexico, the capital, and was henceforth conducted for the United States by General Winfield Scott, whose previous military career had been much the same as General Taylor’s.  Scott had been made Major-General and Commander-in-Chief of the Army in 1841.  His first operation in Mexico was the taking of Vera Cruz, the principal Mexican seaport, on the Gulf of Mexico.  With the aid of a fleet he besieged the city in March, 1847, and on the 27th received its surrender.  At Cerro Gordo (April 17th and 18th) he won an important victory that opened his way through the mountains toward his objective, the city of Mexico.  Reenforcements gradually reached him, and by the first of August he was ready to move on the valley of Mexico with about eleven thousand men.  From this stage to the fall of the capital, completing the conquest of the country, Bonner’s account gives a graphic recital of events.  The city was held by Americans from September 14, 1847, the day they entered it, until the signing of the Treaty of Guadalupe-Hidalgo (February 2, 1848), which ended the war.

With the energy that characterized Santa Anna throughout the Mexican War, he had prepared for a desperate defence.  Civil strife had been silenced, funds raised, an army of twenty-five thousand men mustered, and every precaution taken which genius could suggest or science indicate.  Nature had done much for him.  Directly in front of the invading army lay the large lakes of Xochimilco and Chalco.  These turned, vast marshes, intersected by ditches and for the most part impassable, surrounded the city on the east and the south—­on which side Scott was advancing—­for several miles.  The only approaches were by causeways; and these Santa Anna had taken prodigious pains to guard.  The national road to Vera Cruz—­which Scott must have taken had he marched on the north side of the lakes—­was commanded by a fort mounting fifty-one guns on an impregnable hill called El Penon.  Should he turn the southern side of the lakes, a field of lava, deemed almost impassable for troops, interposed