In the 1840 the United States and Mexico fought over

The Mexican-American War, waged between the United States and Mexico from 1846 to 1848. They were fighting over the Southern Boundary of Texas, in other words the they were fightng over land in the Southwest.

From 1846 to 1848, U. S. and Mexican troops fought against one another in the Mexican-American War. Ultimately, it was a battle for land where Mexico was fighting to keep what they thought was their property and the U. S. desired to retain the disputed land of Texas and obtain more of Mexico's northern lands.