One of the seminal events of American history occurred today in 1846: the begining of the Mexican-American War. The War, overlooked in contemporary classrooms, dramatically altered the American landscape by adding California, New Mexico, Utah, Arizona and Nevada to the Union’s territory (they became states later) and annexing portions of Colorado and Wyoming as well. Because of the growing discontent with Mexico, America sought a quick settlement to the “Oregon Question” and thus a northern border with Canada was established by treaty with Britain; the intended side-effect of this pact virtually eliminated the English desire to claim California for the Crown. In addition to establishing the current borders of the country, it also fueled mistrust between North and South. Many Northerners sought greater expansion into the Oregon Territory to compliment the growth of “free” states while the South saw the acquisition of the Mexican territories as fuel for the addition of “slave” states.
Future players in the Civil War featured prominently in this conflict as well: Congressman Abraham Lincoln was an opponent of the war and his later day counterpart, Jefferson Davis, established himself as a vociferous proponent. Generals Grant, Lee, Meade and Jackson served as comrades and could hardly predict their later adversarial roles. A relatively swift campaign, the American Army marched into Mexico City a few years later after the Nation’s first amphibious assault — hence the “From the Halls of Montezuma…” line in the Marines fight song.
Ironically, amongst the Mexican casus belli was illegal immigration: of Americans into Texas. Texas had already fought its war of independence from Mexico and much of Europe and the United States recognized it as a sovereign entity. Resolutions favoring Texas statehood were perpetually introduced in Congress, but had yet to pass. Texans deeply desired statehood so they encouraged immigration to their new Republic. The Mexican government, which viewed Texas the way Lincoln viewed South Carolina, Virginia et. al during the Civil War, deemed the “illegal” immigration a threat to their country and warned the United States that annexation (or statehood) of Texas meant war. Border skirmishes erupted near the Rio Grande. When the Americans sought to purchase what eventually became the western US from Mexico — and said offer was rebuffed — the Texas skirmishes protracted into a larger war.
In terms of objectives met, the war was enormously successful for the United States. With the Gadsen Purchase a few years later, wherein America acquired additional Mexican territory, the continental borders of the country were set. James K. Polk presided over the war and probably would have easily won a second term, but he walked away from the Presidency having fulfilled his greatest ambition. The war sowed seeds Americans would reap for decades: slavery, the Indian Wars (who turned from opposing Mexico to the US) and, of course, our relationship with our southern neighbor.