In the Battle of Monterrey (September 21-24, 1846) during the Mexican-American War, General Pedro de Ampudia and the Mexican Army of the North was defeated by the Army of Occupation, a force of United States Regulars, Volunteers and Texas Rangers under the command of Zachary Taylor. The Mexican-American War was an armed conflict between the United States of America and Mexico from 1846 to 1848 in the wake of the 1845 U.S. annexation of Texas. Combat operations lasted from spring 1846 to fall 1847. American forces quickly occupied New Mexico and California and then invaded parts of Northeastern Mexico and Northwest Mexico. The Pacific Squadron conducted a blockade, and took control of several garrisons on the Pacific coast in Baja California. After Mexico would still not agree to the cession of its northern territories, another American army captured Mexico City, and the war ended in victory of the U.S. The Treaty of Guadalupe Hidalgo forced Mexican Cession of the territories of Alta California and New Mexico to the U.S. in exchange for $18 million. In addition, the United States forgave debt owed by the Mexican government to U.S. citizens. Mexico accepted the Rio Grande as its national border, and the loss of Texas.