In the early 1840s most of the American public were persuaded that God's given freedom, that they enjoyed, was to be spread out to as much territories as it was possible. Americans saw how their democratic institutions really worked. Therefore, they were determined to take possession of neighboring land and establish the same institutions there. However, besides the political ideals, there was also a greed for land. Most of the members of the Democratic Party were destined to expend the territories of the Untied States. That emotional upsurge was called Manifest Destiny. Although Manifest Destiny was criticized by some people as blatantly racist, it enjoyed support among U.S. citizens and politicians in the mid- and late 1800s. The westward migration of U.S. citizens was encouraged by Manifest Destiny, a belief that territorial expansion by the United States was both inevitable and divinely ordained. Those who believed in Manifest Destiny also believed that the culture of the United States was superior to other cultures and that republican forms of government and democracy should be expanded in order to "civilize" other peoples.
Manifest Destiny was very popular especially during the presidency of James K. Polk (1845-1849). Polk and his administrators sought trade outlets to the Pacific Ocean and were looking into possessing coasts and bays of Texas, Oregon and California. Manifest Destiny was an ideology that became one of the causes for the Mexican conflict.
The events, which lead to the Mexican conflict, started in the state of Texas. Mexico granted the independence to Texas only on the condition that Texas would not attach itself to any other country. However, three days before Polk took office, President Tyler had signed a bill annexing Texas to the United States. This caused Mexico to break off relations with the United States.