The United States fought four wars in the 1800s:

 

The United States fought four wars in the 1800s: the War of 1812, the Mexican-American War, the Civil War, and the Spanish-American War. The United States fought Mexico in the Mexican-American War from 1846 to 1848. The United States wanted to expand west. In 1846, the government of the United States decided it wanted land that belonged to Mexico. Many citizens of the United States and Mexico lived on that land. The United States won the war. The land that was once part of Mexico became part of the United States. That land now forms the states of California, New Mexico, Utah, Nevada, Arizona, and parts of Colorado and Wyoming.