Changes

These events brought within the control of the United States the future states of Texas, California, Nevada, New Mexico, Arizona, Utah, Washington, and Oregon, as well as portions of what would later become Oklahoma, Colorado, Kansas, Wyoming, and Montana.

Following Texas’ successful war of independence against Mexico in 1836, President Martin van Buren refrained from annexing Texas after the Mexicans threatened war. Accordingly, while the United States extended diplomatic recognition to Texas, it took no further action concerning annexation until 1844, when President John Tyler restarted negotiations with the Republic of Texas. His efforts culminated on April 12 in a Treaty of Annexation, an event that caused Mexico to sever diplomatic relations with United States. Tyler, however, lacked the votes in the Senate to ratify the treaty, and it was defeated by a wide margin in June. Shortly before he left office, Tyler tried again, this time through a joint resolution of both houses of Congress. With the support of President-elect Polk, Tyler managed to get the joint resolution passed on March 1, 1845, and Texas was admitted into the United States on December 29.

Believing that he was on the cusp of an agreement with the Mexicans, Trist ignored the recall order and presented Polk with the Treaty of Guadalupe-Hidalgo, which was signed in Mexico City on February 2, 1848. Under the terms of the treaty, Mexico ceded to the United States approximately 525,000 square miles (55% of its prewar territory) in exchange for a $15 million lump sum payment, and the assumption by the U.S. Government of up to $3.25 million worth of debts owed by Mexico to U.S. citizens.

While Polk would have preferred a more extensive annexation of Mexican territory, he realized that prolonging the war would have disastrous political consequences and decided to submit the treaty to the Senate for ratification. Although there was substantial opposition to the treaty within the Senate, on March 10, 1848, it passed by a razor-thin margin of 38 to 14.