In 1845, President John Tyler signed a Congressional resolution to annex Texas, and by 1846, 4,000 troops were on the Rio Grande. Shortly thereafter, President James Polk proposed that Mexico sell its northern half to the U.S. Hostilities commenced and the U.S. crossed the border to occupy Matamoras, U.S. warships landed troops at Veracruz, who fought their way overland to Mexico City. Santa Anna led a defending army, but the Mexicans were overwhelmed....