Why did the U.S. go to war with Mexico?
Texas broke off from Mexico, the Mexicans tried to take it back by force and lost… in the Treaties of Velasco (1836) signed at the end of that war, Texas’ border was set at the Rio Grande River. The Mexican government in 1846 THEN changed their mind and moved the border north 150 miles… Mexican troops ambushed and killed members of a US Cavalry troop, and then laid siege to Fort Brown. President Polk then went to Congress and sought a declaration of war. Howerver use of the term “Manifest Destiny’ is correct: The term was first used primarily by Jacksonian Democrats in the 1840s to promote the annexation of much of what is now the Western United States (the Oregon Territory, the Texas Annexation, and the Mexican Cession).
