In 1853, President Franklin Pierce wanted to build the transcontinental railroad that would connect the southern states to the Pacific coast. He also wanted to settle a territorial dispute they continue to exist with Mexico after the Mexican war. So, he sent ambassador James and Gadsden to Mexico to negotiate a land deal.

In the arrangement, called the Gadsden purchase, the United States agreed to pay Mexico $10 million in exchange for a roughly 30,000 mi.² expanse of land in what would become the state of Arizona and New Mexico. This purchase establish the southern border of the United States that we are familiar with today. And also provided an ideal path for a southern transcontinental railroad.

Before the purchase could be finalized, it had to be approved by Congress. The rising tensions between north and south over the issue of slavery made it difficult to come to any sort of disagreement. Northerners thought the real reason for the purchase was to add more slave territory. As a result, the purchase involves a smaller piece of land then it was originally planned.

In 1854, Congress was able to come together to finalize the Gadsden Purchase. The Southern Transcontinental Railroad would not be completed, however, until 1883.