On November 10, 1845, before hostilities broke out, President James K. Polk sent his envoy John Slidell to Mexico. Slidell was ordered to offer Mexico about $5 million for the nuevo México territory and up to $40 million for Alta California.  The Mexican government fired Slidell and refused to meet with him at all.  Earlier this year, Mexico severed diplomatic relations with the United States, in part on the basis of its interpretation of the Adams-Onís Treaty of 1819, in which newly independent Mexico claimed to have inherited rights. In this agreement, the United States had “forever” renounced any claim to Spanish territory.   Map of the United States, including lands acquired by the Treaty of Guadalupe Hidalgo, which accompanied President Polk`s annual message to Congress in December 1848 After the defeat of the Mexican army and the fall of Mexico City in September 1847, the Mexican government capitulated and peace negotiations began. The war officially ended with the signing of the Treaty of Guadalupe Hidalgo in Mexico on February 2, 1848. The treaty added an additional 525,000 square miles to U.S. territory, including the lands that make up all or part of present-day Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming. Mexico also renounced any claim to Texas and recognized the Rio Grande as America`s southern border.
In return, the United States paid $15 million to Mexico and agreed to settle all claims of U.S. citizens against Mexico. Treaty of Guadalupe Hidalgo (February 2, 1848), a treaty between the United States and Mexico that ended the Mexican War. It was signed in Villa de Guadalupe Hidalgo, a neighborhood in the north of Mexico City. The treaty draws the boundary between the United States and Mexico on the Rio Grande and the Gila River; For a payment of $15,000,000, the United States received more than 525,000 square miles (1,360,000 square kilometers) of land (now Arizona, California, western Colorado, Nevada, New Mexico, Texas and Utah) from Mexico and agreed in return to settle the more than $3,000,000 in claims by U.S. citizens against Mexico. With this annexation, the continental expansion of the United States was completed with the exception of the lands added in the Gadsden Purchase (1853). In addition to the sale of land, the treaty also provided for the recognition of the Rio Grande as the border between the state of Texas and Mexico.  The boundaries of the lands were established by a survey team composed of designated Mexican and American officials and published in three volumes as The United States and Mexican Boundary Survey.
On December 30, 1853, countries unanimously changed the border from the original border by increasing the number of border marks from 6 to 53.  Most of these marks were simply piles of stones.  Two subsequent conventions, 1882 and 1889, further clarified the boundaries, as some of the marks had been moved or destroyed.  Photographers were called in to document the position of the markers. These photos can be found in Recording Group 77, Documents of the Office of Chief Engineers, at the National Archives. Trist sent a copy to Washington with the fastest funds available, forcing Polk to decide whether or not to reject the highly satisfying manual labor of his discredited subordinate. Polk decided to forward the contract to the Senate. When the Senate reluctantly ratified the treaty on March 10, 1848 (by a vote of 34 to 14), it suppressed Article X, which guaranteed the protection of Mexican land allocations. After ratification, U.S.
troops were withdrawn from the Mexican capital. Mexican officials and Nicholas Trist, President Polk`s representative, began talks on a peace treaty in August. On February 2, 1848, the treaty was signed in Guadalupe Hidalgo, a town north of the capital from which the Mexican government had fled as American troops advanced. Its regulations required Mexico to cede 55% of its territory (now Arizona, California, New Mexico and parts of Colorado, Nevada and Utah) in exchange for fifteen million dollars in compensation for war damage to Mexican property. The treaty was then signed on 10 September. It was ratified by the U.S. Senate in March 1848 by 38 votes to 14 and by Mexico on May 19, 1848 by 51 votes to 34 and a Senate by 33 to 4. The news that the New Mexico Legislature had just passed legislation to organize a U.S. agreement. The territorial government has helped allay Mexicans` concerns about the imclassification of New Mexico`s population.
 The treaty was officially promulgated on July 4, 1848.  On May 30, 1848, when the two countries exchanged ratification of the Treaty of Guadalupe Hidalgo, they negotiated a protocol with three articles to explain the amendments. The first article noted that the original Article IX of the Treaty, although replaced by Article III of the Louisiana Treaty, would still confer the rights described in Article IX. The second article confirmed the legitimacy of land allocation under Mexican law.  The Treaty of Guadalupe Hidalgo was signed by the United States and Mexico on February 2, 1848, ended the Mexican War (1846-48), and extended the borders of the United States by more than 525,000 square miles. In addition to the establishment of the Rio Grande as the border between the two countries, the territory acquired by the United States became. included the remaining states of Texas, California, Nevada, Utah, most of New Mexico and Arizona, and parts of Colorado and Wyoming. .