The Mexican-American War
The war between Mexico and the United States had its beginnings with the struggle over who would control Texas.
American settlers began moving to the Texas territory in the 19th Century, after the Revolutionary War had been won and the exploration of lands west of the Appalachian Mountains had begun.
The Louisiana Purchase had stretched the western boundaries of the United States farther west than they had ever been. After the success of Lewis and Clark, more and more Americans explored and settled in the Louisiana Territory.
And right next to Louisiana was Texas.
Texas was big land, rich with resources and possibilities. It was also largely part of Mexico.
As more and more Americans moved to the Texas territory, the cry grew for Texas to be part of the U.S. This began to happen in 1835, when Texas declared itself independent from Mexico. The Texas Republic was born, and its first president was Sam Houston. The secretary of state of this new republic was Stephen F. Austin, who had been a pioneer in helping settle the Texas territory.