The rapid settlement of the Old Northwest and Southwest resulted in the admission of Illinois, Alabama, Indiana, Mississippi states to the Union in close succession between 1816 and 1819.
Trade with the United States was opened when Mexico won its independence from Spain in 1821 and New Mexico was made a territory of Mexico.
The following year, American settlers started traveling the Santa Fe Trail to reach New Mexico.
The Mexican-American War broke out in 1846, and U.S. General Stephen W.
Land was easy to come by in the West while it was heavily populated in the East and South.
Many white Americans left the East due to population expansion.