On the night of May 9 , 1846 , Frémont received Receiving a message brought Bringing to him by Lieutenant Archibald Gillespie , from President James Polk about the possibility of war Hostile_encounter with Mexico .

In 1845 , newly elected Choosing U.S. President James K. Polk , who saw the annexation of Texas as the first step towards a further expansion of the United States , sent Sending troops to the disputed area and a diplomatic mission to Mexico .

The victory and territorial expansion Polk envisioned inspired Influence great patriotism in the United States , but the war and treaty drew some criticism Judgment_communication in the U.S. for their casualties , monetary cost , and heavy-handedness , particularly early on .

A massive assault Attack by the corps of Maj. Gen. William J. Hardee , followed by that of Leonidas Polk , overran the wing commanded Control by Maj. Gen. Alexander M. McCook .