Expansion westward seemed perfectly natural to many Americans in the mid-nineteenth century. Like the Massachusetts Puritans who hoped to build a "city upon a hill, "courageous pioneers believed that America had a divine obligation to stretch the boundaries of their noble republic to the Pacific Ocean. Independence had been won in the Revolution and reaffirmed in the War of 1812. The spirit of nationalism that swept the nation in the next two decades demanded more territory. The "every man is equal" mentality of the Jacksonian Era fueled this optimism. Now, with territory up to the Mississippi River claimed and settled and the Louisiana Purchase explored, Americans headed west in droves. Newspaper editor John O'Sullivan coined the term "manifest destiny" in 1845 to describe the essence of this mindset.
The religious fervor spawned by the Second Great Awakening created another incentive for the drive west. Indeed, many settlers believed that God himself blessed the growth of the American nation. The Native Americans were considered heathens. By Christianizing the tribes, American missionaries believed they could save souls and they became among the first to cross the Mississippi River.
Economic motives were paramount for others. The fur trade had been dominated by European trading companies since colonial times. German immigrant John Jacob Astor was one of the first American entrepreneurs to challenge the Europeans. He became a millionaire in the process. The desire for more land brought aspiring homesteaders to the frontier. When gold was discovered in California in 1848, the number of migrants increased even more.
At the heart of manifest destiny was the pervasive belief in American cultural and racial superiority. Native Americans had long been perceived as inferior, and efforts to "civilize" them had been widespread since the days of John Smith and Miles Standish. The Hispanics who ruled Texas and the lucrative ports of California were also seen as "backward."
Expanding the boundaries of the United States was in many ways a cultural war as well. The desire of southerners to find more lands suitable for cotton cultivation would eventually spread slavery to these regions. North of the Mason-Dixon line, many citizens were deeply concerned about adding any more slave states. Manifest destiny touched on issues of religion, money, race, patriotism, and morality. These clashed in the 1840s as a truly great drama of regional conflict began to unfold.