John L. O'Sullivan was a newspaper editor who first used the term manifest destiny in reference to the annexation of Texas and the Oregon Territory. He titled an essay in an 1845 edition of the Democratic Review "Annexation." In it, he argued against opposition to the annexation of Texas on the grounds of divine right. In other words, he declared that the United States must annex Texas because it was the will of God. According to O'Sullivan, the United States had a divine mission to spread democracy throughout the North American continent.

One of the factors delaying the annexation of Texas was disagreements between pro-slavery and anti-slavery factions of Congress. According to O'Sullivan, these differences should be put aside in view of God's mandate to white Americans to spread over and subdue the continent. Although O'Sullivan coined the term manifest destiny to describe what was perceived as the inevitability of white America's expansion towards the West Coast, he was not the first to embrace the concept. As far back as 1823, President James Monroe gave a speech to Congress in which he announced that any attempt by European powers to hinder US expansion westward would be considered a hostile act. This became known as the Monroe Doctrine. Even further back, many early European settlers were convinced that God had given them inherent superiority and that it was their divine duty to remove impediments such as Native Americans that might stand in their way in the colonization of the New World.

In fact, the same year that John L. O'Sullivan wrote his now-famous articles, President John Tyler signed an annexation bill. On December 29, the new president, James Polk, signed a bill confirming the annexation, and on February 19, 1846, Texas formally became a part of the United States.