On February 2, 1848, the Treaty of Guadalupe Hidalgo was signed in Mexico without President James K. Polk’s knowledge. The United States acquired about 55 percent of Mexico’s territory for $15 million.
The treaty was eventually endorsed by Polk and sent to the Senate for confirmation, where it was approved by a 34-14 vote on March 10, 1848. The Senate amended the treaty to delete a guarantee of Mexican land grants, particularly in Texas.
The treaty set a border between Texas and Mexico, and ceded land that now includes the states of California, Nevada, Utah, New Mexico, most of Arizona and Colorado, and parts of Oklahoma, Kansas, and Wyoming to the United States.
Abolitionists had objected to the Mexican-American War and the treaty resulting from it as an expansion of slavery. The powerful Whig leader in the Senate, Daniel Webster, opposed it, as did a young Representative from Illinois, Abraham Lincoln. Also in the House, former President John Quincy Adams led the fight against the war in Mexico. Adams died from complications of a stroke he suffered on the House floor after he objected to a resolution honoring the Mexican-American War.
Polk’s initial objections to the treaty included his desire to have Baja California and property to the Baja’s east as part of the treaty, a wish he had communicated that desire to negotiator Nicholas Phillip Trist. But he lobbied heavily of its approval in the Senate.
Trist was the chief clerk to Secretary of State James Buchanan, and he had been sent to Mexico in 1847 to work with General Winfield Scott to negotiate a settlement. Polk’s orders to recall Trist
Polk also wanted the talks to take place in Washington, and he sent orders to Mexico that Trist had been recalled as the treaty negotiator. During the six weeks it took for Polk’s orders to make their way to Trist, the diplomat realized he had a brief period to negotiate a treaty with the unstable government in Mexico.
Trist ignored the recall order and the Treaty of Guadalupe Hidalgo was signed in Mexico without Polk’s knowledge. Trist sent a copy of the treaty by the fastest means possible to Polk. On Trist’s return to Washington, he was promptly fired by Polk and denied any salary earned during treaty negotiations.
In late 1853, the United States acquired more territory from Mexico. The Gadsden Purchase represented about 29,000 square miles of land that eventually became southern Arizona and New Mexico. The then-steep cost of $10 million became part of a broader controversy about slavery since Southern railroad interests wanted the territory for a proposed rail line to California.