The conflict expended American territorial claims westward to California from the Rio Grande which divides portions of Northern Mexico with the state of Texas. The war was controversial for being a blatant land grab condoned by then President Polk. Political theorists will note that Henry David Thoreau’s Civil Disobedience was written as a response to this war, slavery, and also the selfish streak typifying American individualism. Thoreau’s refusal to pay taxes is a model for civil disobedience against unjust wars and an unjust government. Gandhi’s Satyagraha, Nelson Mandela, and Martin Luther King Jr’s campaigns were profoundly influenced by Thoreau’s work. Draft dodgers of the Vietnam war era as well as draft dodgers of the Iraq War 2003 follow from Thoreau’s complaint that “… There are thousands who are in opinion opposed to slavery and to the war, who yet in effect do nothing to put an end to them.””

The Mexican-American War also produced some of the technological changes as well as the political turmoil that eventually led to the American Civil War. Unsettled disagreements concerning state-level rights over slavery were further exacerbated by an increasing militarism. To be American President, one necessarily had to have commanded forces into battle. War continues to define the American national politics. The war was extremely unbalanced with American victories recurring against a technologically disadvantaged Mexican opponent. Mexico was also politically fragmented. The other, most obvious consequence is that California, New Mexico, Arizona are American states.