The Gadsden Purchase was an agreement between Mexico and the United States that was finalized in 1854. In the treaty, Mexico agreed to cede Arizona, California, and New Mexico for $10 million. It helped the United States have enough land for the southern transcontinental railroad and helped resolve conflicts generated from the Mexican American War. However, this increased US internal tensions between the North and South, as the northerners believed that the purchase would provide an imbalance in Congressional representation of pro and anti-slavery parties.