The annexation of Texas leads to war with Mexico, which is concluded by the Treaty of Guadalupe Hidalgo. In it, Mexico agrees to sell to the United States a vast territory covering the future states of California, Arizona, New Mexico, Nevada, Utah, Wyoming and Colorado. Although President James K. Polk had not authorized the negotiations that led to the treaty, he submits it to the Senate, which passes it by a vote of 38-14. An effort by anti-slavery senators to attach to the treaty the Wilmot Proviso, banning slavery from the new territory, fails 38-15.