It was known as the Gadsden Purchase (1853), and it included present-day New Mexico and Arizona, south of the Gila River.
You mean before the Mexican-American War? That was the Nueces Strip.
Utah Territory wasn't formed from any state. The land was purchased from Mexico and simply called "Mexican Territory" previously.
The Gadsden Purchase of 1853, named for ambassador James Gadsden, was for a strip of Mexican land which the US bought in order to build a transcontinental railroad through it and to settle some of the border issues between the US and Mexico.
The land between the Appalachian Mountains and the Mississippi river was called the Louisiana Purchase after the Revolutionary War. The Louisiana Purchase was 530,000,000 acres of territory in North America that the United States purchased from France in 1803 for $15 million.
US-Mexico border
buffer state
Jefferson purchased "Louisiana" from France in 1803.
The Mexican Cession.
Indeed. However, it is not called 'secession' but "Mexican Cession".
The Mexican War between the United States and Mexico began with a Mexican attack on American troops along the southern border of Texas on Apr. 25, 1846. By the clash between two patrolling armies called the Thornton Affair.
Central America
Santa Fe trail