On December 30, 1853, the United States and Mexico established their existing border with the completion of the Gadsden Purchase. Only five years after the United States acquired most of the present-day states of California, Arizona, Utah, and Nevada following the Mexican-American War, the U.S. completed the Gadsden Purchase for $10 million. The Gadsden Purchase provided the U.S. with what is now southern Arizona and southwestern New Mexico.

Originally, the U.S. wanted to build a transcontinental railroad through the new territory, using slave labor. The debate over slavery was already so contentious that the project received no federal funding, and the first transcontinental railroad was ultimately built farther north.

acquire
Verb

to get or take possession of.

Noun

natural or artificial line separating two pieces of land.

establish
Verb

to form or officially organize.

transcontinental railroad
Noun

railroad that spans an entire continent.