It stemmed from the annexation of the Republic of Texas by the U.S. in 1845 and from a dispute over whether Texas ended at the Nueces River (the Mexican claim) or the Rio Grande (the U.S. claim).
Moreover, was the Mexican American war justified?
Ultimately, the war was not justi- fied for three big reasons: President Polk provoked it, America was just being greedy, and it meant the expansion of slavery. The war was not justified because President James Polk provoked the Mexican army into fighting. By May of 1846 Texas had become part of the United States.
Simply so, why wasnt the Mexican war justified?
By doing so, the US started a war with Mexico that was justified for illegitimate reasons. The Mexican-American War was not justified because the US took Mexico’s land for the expansion of slavery, and justified their taking advantage of Mexico when it was politically weak by hiding behind Manifest Destiny.