“Introduction” Relations between the United States and Mexico got spoiled in December 1845, when Congress voted to let Texas to be the twenty-eighth state. A negotiated settlement to the Texas boundary (now a disputed international border between the United States and Mexico) was complicated by common changes in Mexican leadership during 1845-46. vs.
How it began After the Mexican government refused to meet with an American representative sent to negotiate the purchase of Mexican lands stretching northward from Texas to the Oregon Country in January 1846, Polk ordered U.S. troops into the territory on the north bank of the Río Grande. The conflict occurred on April 25, 1846, when a Mexican calvary crossed the Río Grande and fought with the American forces. General Zachary Taylor on campaign during the Mexican Cession
How it began(part 2) During the nearly two years of war, American troops took possession of Mexican territory in what is now California, New Mexico, northern Mexico, and the capital, Mexico City. The Treaty of Guadalupe Hidalgo, which ended the war in February 1848, established boundaries for the United States and Mexico. Under the terms of Guadalupe Hidalgo, Mexico ceded to the United States an immense territory of nearly one million square miles, including land in what is now California, Nevada, Utah, New Mexico, Arizona, Colorado, Wyoming, Oklahoma, and Kansas. The United States, in turn, agreed to pay Mexico $15 million and assume $3.25 million in debt claims against Mexico. The treaty also provided that Mexican people who remained on their lands would be granted American citizenship and allowed to retain their property.
Losing territory Mexico lost much of its territory in the war, leaving it with a lasting bitterness towards the United States. Santa Anna fled to exile in Venezuela. General Porfirio Díaz, President of Mexico from 1877–1911, would later lament: "¡Pobre México! Tan lejos de Dios, y tan cerca de los Estados Unidos." ("Poor Mexico! So far from God, and so close to the United States.") General Taylor on Horseback at the Battle of Buena Vista, February 23, 1847
New western lands In the United States, victory in the war brought a new western lands –the country had also acquired the southern half of the Oregon Country in 1846 – seemed to fulfill citizens' belief in their country. The war made a national hero of Zachary Taylor, a Southern men, who was elected president in the election of 1848.
If you were Mexican you could becomea US Citizen if you lived in that area The treaty also said that Mexicans who stayed in the state would be permitted to become U. S. citizens, and that they would be allowed to keep their land. However, the treaty was never fully honored. In the decades following the signing of the treaty, Mexican-Americans owned nearly 20 million acres of their land by American businessmen, ranchers and railroad companies, as well as by the U.S. Department of the Interior and Department of Agriculture.