Manifest Destiny drove a sense of purpose and established the United States' domination in North America. It also reflected and helped spread the overall pride of being an American at the time.
John L. O'Sullivan, an influential writer and democrat, first coined the phrase "Manifest Destiny" in 1845. It caught on and became the rallying cry for the nation, as it was believed that it was destiny for the expansion of the country. It was used by politicians and publicized in advertisements within newspapers to gain momentum.
For instance, Manifest Destiny is thought to have spurred the U.S. war against Mexico in 1846, which resulted in the attainment of what is now known as the Southwestern region of the U.S.