What was the gasdsden purchase

In short, The Gadsden Purchase was a Treaty between the United States and Mexico that gave the US 29,670-square-miles,  Below I will include more informaiton!

Explanation:

The Gadsden Purchase was also known as the Sale of La Mesilla (or as they called it in Mexico, the Venta de La Mesilla). It was treaty called Treaty of Mesilla, where the United States gained the territory of present day Arizona. The US wanted this land to build the transcontinental railroad. It was formally put into effect on June 8th, 1845, and, the first draft for this treaty was signed by James Gadsden, who at the time was the U.S. ambassador to Mexico, and it was also signed by Antonio López de Santa Anna, who at the time was the president of Mexico.

Hope this helps! :)