Presidential term: March 4, 1845 – March 4, 1849
Just before Tyler finished his four years’ term, therefore, Congress decided to admit Texas (1845); but as a dispute soon arose about its southern boundary, the eleventh President, James K. Polk, found himself with a war on his hands. Many good Americans say that Texas had no right to claim the land between the Nueces River and the Rio Grande, and that this was an unfair and needless war, but others claim that it was for the best.
The President Polk began his term by sending General Zachary Taylor down to Texas to occupy the disputed strip of land. There he was met by the Mexicans, who attacked the American troops. A skirmish took place, blood was steed, and soon after war was declared. Instead of waiting until more troops could join him, Taylor pressed on, and, meeting the Mexicans at Palo Alto and Resaca de la Palma, near the mouth of the Rio Grande, he defeated them both times, in spite of their superior numbers.
The Mexicans having fled over the Rio Grande, Taylor pursued them, took Matamoros, and began to besiege Monterey. This place, too, was carried, though defended by a garrison of about ten thousand men. In the meantime, two other armies had been sent out; so the Mexicans were obliged to defend themselves not only against Taylor in the north, but also against General Scott, who took his army by sea to Vera Cruz, and marched thence across country toward the city of Mexico. The third American army, under Colonel Stephen W. Kearny, was directed toward New Mexico and California, both of which belonged to Mexico at that time, and included all the land from the Pacific Ocean to Texas and the Rocky Mountains, up to the parallel of 42°.