On October 14, former U.S. General William Walker leads a mercenary force of 150 Americans who join with local rebels to conquer Nicaragua. Walker serves as president from July 12, 1856 to May 1, 1857. He legalizes slavery there.

The Mexican War ends on February 2, with the signing of the Treaty of Guadalupe Hidalgo. That agreement gives the United States jurisdiction over nearly half of what was Mexico including the current states of California, New Mexico, Arizona, Nevada, Utah and part of Colorado.