What is the Gadsden Purchase about and what did it do? ( 5-7 or at least a paragraph plz)

In 1853, the Mexican government kicked Americans out of the territory. ... Congress ratified a revised version of the treaty; the U.S. would purchase just over 29 thousand square miles of land in exchange for $10 million. The Gadsden Purchase secured area for the transcontinental railroad and set the U.S.-Mexican border.