maifest destiny changed the united states majorly in the 1800's significantly. westward expansion played a big role in this.
A major role in manifest destiny was James K. Polk. He achieved his goal, which was gaining more territory for the U.S. He got the Oregon territory while being president.
during the 1800s america went to war against Mexico for the texas land. America won the war and got 7 states including texas, Arizona, Califorina, Colorado, Nevada, Mew Mexico, Utah and whyoming