Mexican-American
War (apr 25, 1846 – feb 2, 1848)
Description:
At this time, the current president of the U.S. was James K. Polk. The Mexican leadership still considered Texas to be it's northeastern province and never acknowledged the independent Republic of Texas. (Src: https://en.wikipedia.org/wiki/Mexican%E2%80%93American_War)
Added to timeline:

Westward Exp. Timeline
Date: