The Treaty of Guadalupe Hidalgo was a peace treaty that ended the
Mexican-American War (1846–1848).  The treaty provided for the Mexican Cession,
in which Mexico ceded 1.36 million km² (525,000 square miles) to the United States
in exchange for USD$15 million. The United States also agreed to take over $3.25
million in debts Mexico owed to American citizens.

The cession included parts of the modern-day U.S. states of Colorado, Arizona,
New Mexico, and Wyoming, as well as the whole of California, Nevada, and Utah.
The remaining parts of what are today the states of Arizona and New Mexico were
later ceded under the 1853 Gadsden Purchase.

The treaty was signed by Nicholas P. Trist on behalf of the United States and
Luis G. Cuevas, Bernardo Couto, and Miguel Atristain as plenipotentiary representatives
of Mexico on February 2, 1848, at the Villa de Guadalupe Hidalgo (today
Gustavo A. Madero, D.F.), slightly north of Mexico City. It was subsequently
ratified by the United States Senate on March 10 and by the Mexican government
on May 19; the countries' ratifications were duly exchanged on May 30, 1848, at
the city of Santiago de Querétaro.

However, the version of the treaty ratified by the United States Senate eliminated
Article 10, which stated that the U.S. government would honor and guarantee all
land grants awarded in lands conquered by the United States to citizens of Spain
and Mexico by those respective governments. Article 8 guaranteed that Mexicans
who remained more than one year in the conquered lands would automatically become
full-fledged American citizens (or they could declare their intention of remaining
Mexican citizens); however, this Article was effectively weakened by Article 9,written
into the treaty by the U.S. Senate, which stated that Mexican citizens would "be
admitted at the proper time (to be judged of by the Congress of the United States)."