In the early decades of the 19th century, USA leaders were quite keen on expanding the country westwards to sustain its then growing population. Notably, discussions of slavery in the then newly acquired territories colored discussions regarding the Western frontier. The Missouri Compromise (MC), which was formulated in 1820 allowed from the admission of both free and slave states in the West to the union. Notably, the MC was not applied to the then newly-acquired states not covered by the Louisiana Purchase (LP). Despite the 1930s sectional conflict in the West, more and more Americans continued migrating to it. In mid-1837, Texan American settlers and Tejanos became independent of Mexico. Mexican and Texas’ annexation, even then, only became a hot political issue in 1844, during James Polk’s presidency. Polk was an expansionist.
In 1846, Texas and Oregon joined the union as slave and free states respectively. In mid-1848, the Mexican War was brought to an end by the TGH (Treaty of Guadalupe Hidalgo). The TGH bequeathed the union an additional territory measuring a million square miles. The additional territory led to the resurgence of the question previously settled by the MC. In 1854, Stephen Douglas proposed the establishment of Nebraska along with Kansas with the LP. According to the MC, however, the two states were to be free of slavery. Contestations between those supporting slavery and those against it in Kansas plunged the state into war. The war gave rise to a countrywide civil war over the question of slavery as well.
The development of the Manifest Destiny doctrine added to sectional conflict in varied ways. First, the doctrine amplified the conflict between Southerners and Northerners on the question of slavery (Mayer, 1998). Second, owing to the doctrine increased the struggle between the South and North for legislative representation. Each of the two regions sought to have advantages over the other with regard the enactment of principal legislations. Third, owing to the doctrine, Northerners were in support of import tariffs while the Southerners resented them (Mountjoy, 2009).