During the Mexican–American War, the United States and Mexico were at loggerheads over the land which Texas covers. This was after Mexico and the U.S. both wanted to annex the Texan state. In 1845, Mexico had claimed that Texas ended at the Nueces River, while the United States claimed the Rio Grande, which was the root of the dispute. Fighting continued for the next two years as General Taylor led his troops to Monterrey, and General Stephen Kearny and his men went to New Mexico, Chihuahua, and California. General Winfield Scott and his army delivered the decisive blow as they captured Mexico City in August 1847.

Mexican officials and Nicholas Trist, the U.S. representative, began discussions for a peace treaty in August 1847. On February 2, 1848, the Treaty was signed in Guadalupe Hidalgo, to which the Mexican leaders had fled ahead of the American troops.

With the treaty of Guadalupe Hidalgo, America emerged victorious, gaining 525,000 square miles of Mexican territory from the Rio Grande to the Pacific Ocean. The southern American boundaries: Arizona, Nevada, Colorado, New Mexico, California, Utah, and Wyoming are the present-day names of the land acquired as a result of the Treaty. With the land also came the Mexican people who lived there, who could choose to become American citizens within a year — of which 90% did.

According to nationaltoday.com. Source of photos: internet