The idea of manifest destiny was not a new one before John O’Sullivan coined the phrase in his essay “Annexation”, published in The United States Magazine and Democratic Review in 1845. The process of westward expansion had been ongoing since the British defeat of the French in in 1763. By the early nineteenth century, westward expansion became more embedded in American policy, especially after the Louisiana Purchase in 1803.

Therefore, it is important to understand that the idea of manifest destiny was present in United States expansionism during the first part of the nineteenth century. Many leading Americans, including President Andrew Jackson, justified their policies of westward expansion with the rhetoric of American freedom. This inevitably involved removing obstacles to that "freedom," such as the various indigenous tribes which occupied the lands to the west, or indeed foreign nations like Mexico. By 1846, the term "manifest destiny" had been adopted by both supporters and critics of this policy, especially in the context of the annexation of Texas, which would ultimately lead to war.

O’Sullivan explicitly linked the idea of manifest destiny to American freedom by suggesting that it was inevitable that the West would be populated by white Anglo-Saxon Americans in order to spread their “American experiment” of democracy and freedom into the uncivilized world. He saw the civilizing forces of westward expansion as a way in which white Americans could continue to be the perfect example of a free and just society. He argued that their democratic system and the freedoms that white Americans enjoyed proved that they were morally and intellectually superior. O’Sullivan suggested that manifest destiny would provide opportunities for more people to live free and independent lives. In his article, he wrote,

“They will necessarily become independent. All this without the agency of our government, without responsibility of our people—in the natural flow of events . . . . And they will have a right to independence—to self-government—to the possession of the homes conquered from the wilderness by their own labors and dangers, sufferings and sacrifices. . . . Whether they will then attach themselves to our Union or not, is not to be predicted with certainty.”

His connections to ideas of American freedom were so explicit that supporters of the expansion of slavery raised concerns about manifest destiny only applying to Northern states. Richard Winthrop reflect these fears when he commented that manifest destiny only existed in the “Yankee nation."

Although the term was not attributed to O’Sullivan until 1927, many writers, artists and social commentators made this very connection between manifest destiny and freedom. In 1874, John Gast’s painting American Progress demonstrates this, as the central figure is a representation of the very ideals of freedom and democracy that O’Sullivan wrote about in 1846. Therefore, it is clear that O'Sullivan's connections between manifest destiny and American freedom had a lasting impact.

John O'Sullivan, writing in 1839, made a strong correlation between American exceptionalism, freedom, and manifest destiny. In other words, he believes that America's love of liberty makes it unique and destined to do great things on the continent. He cites the nation's founding document to support his claim:

Declaration of National Independence being entirely based on the great principle of human equality, these facts demonstrate at once our disconnected position as regards any other nation; that we have, in reality, but little connection with the past history of any of them, and still less with all antiquity,.....

O'Sullivan also believes that a country's destiny is determined by the level of freedoms that it allows its citizens. In making the earlier case that the United States is the leader in civil liberties, this passage assures the reader that the United States has a positive future.

It is so destined, because the principle upon which a nation is organized fixes its destiny, and that of equality is perfect, is universal........its greatness, its duration, were always proportionate to the democratic equality in its system of government. . .

He finally connects his argument that the United States is destined to dominate the continent because of the unbridled freedoms that are granted to its citizens:

America is destined for better deeds. It is our unparalleled glory that we have no reminiscences of battle fields, but in defence of humanity, of the oppressed of all nations, of the rights of conscience, the rights of personal enfranchisement.