The North and the South had stereotyped one another and each group thought they were doing everything much better than the other was. The major problem they were having was how to handle the issue of slavery in the territories.
President Polk was unaware that his desire for expansion would eventually divide the Whig party, and bring to the open an aggressive southern theory on slavery in the territories. In 1846 the Oregon Treaty was signed giving the United States all of present-day Oregon, Washington, and Idaho and parts of Wyoming and Montana. Polk had American troops defending the border of Texas and tried to purchase a huge tract of land from the already angry Mexicans. They refused and Polk decided to ask Congress for a declaration of war. Mexican forces attacked American troops on disputed territory and Americans died before he had the chance to give his list of grievances to congress.
Polk declared that "war exists by the act of Mexico itself." (Norton et. al., 1999)
The Treaty of Guadalupe was signed following the war of Mexico. The United States gained California and New Mexico (including present-day Nevada, Utah and Arizona) and the Rio Grande was recognized as the border of Texas. The war also brought much controversy. Whigs in congress accused Polk of provoking an unnecessary war. Others charged that the war was a plot to extend slavery. In August 1846, David Wilmont, a Pennsylvania Democrat, proposed an amendment that neither slavery nor involuntary servitude shall ever exist in any territory gained from Mexico. His idea did not pass both houses of congress but it immediately transformed the debate.
The slavery question divided northerners and southerners and could not be kept out of national politics. Slavery was the main topic in the presidential election of 1848. The...