13 May 1846. Although fighting had begun days earlier, Congress officially declared war on Mexico on this date. The struggle cost the lives of 11,300 American soldiers and resulted in the annexation by the US of land that became parts of Oklahoma, New Mexico, Arizona, Nevada, California, Utah and Colorado. The war ended in 1848. Read more at http://www.pbs.org/kera/usmexicanwar/.
Image: By Excel23 – Own work, CC BY-SA 4.0,