The war between the United States and Mexico had two basic causes. First, the desire of the U.S. to expand across the North American continent to the Pacific Ocean caused conflict with all of its neighbors; from the British in Canada and Oregon to the Mexicans in the southwest and, of course, with the Native Americans. Ever since President Jefferson's acquisition of the Louisiana Territory in 1803, Americans migrated westward in ever increasing numbers, often …showed first 75 words of 1353 total…

…showed last 75 words of 1353 total…to win the Presidency in 1848. A true irony is that President Polk, a Democrat, pushed for the war that led to Taylor, a Whig, winning the White House. 4. Relations between the United States and Mexico remained tense for many decades to come, with several military encounters along the border. 5. For the United States, this war provided a training-ground for the men who would lead the Northern and Southern armies in the upcoming American Civil War.