“What about building a “New Mexico City” on the border with Mexico”
I was thinking about Gadsdenland - a small part of the 29,600 square miles purchased.
“U.S. Minister to Mexico James Gadsden, and three envoys of the President of Mexico General Antonio López de Santa Anna Pérez de Lebrón, signed the Gadsden Purchase, or Gadsden Treaty, in Mexico City on December 30, 1853. Santa Anna needed money to help defray expenses caused by the Mexican War and ongoing rebellions, so he sold land to the United States. The treaty, amended and finally approved by the U.S. Senate on April 25, 1854, settled the dispute over the exact location of the Mexican border west of El Paso, Texas, giving the U.S. claim to some 29,600 square miles of land, ultimately for the price of $10 million. The land is what is now southern New Mexico and Arizona.”
https://www.loc.gov/item/today-in-history/december-30/
https://constitutioncenter.org/blog/the-gadsden-purchase-and-a-failed-attempt-at-a-southern-railroad
It sure would suck for people who legitimately own land there.