the Mexican American war started with texas fighting against Mexico for their independence
texas eventually won the war for its independence
now that Texas had their freedom they had problems deciding whether to join the u.s or staying as a free country.
eventually texas chose to join the u.s. but now the problem was whether the u.s was going to annex texas because they already had an equal amount of states that allowed slavery than states that didn't allow slavery. another thing was that qtexas had a lot of dept.
eventually, the u.s annexed texas. Mexico, as you can imagine, wasn't very happy. so they went to war