How does O'Sullivan describe the future realm of the U.S.?
In 1845, columnist John O'Sullivan wrote an essay in favor of adding Texas to the United States. In this essay, he coined the term "manifest destiny" to refer to America's God-sanctioned future of geographical expansion.
In this essay, O'Sullivan already predicts American expansion into California as he writes:
Already the advance guard of the irresistible army of Anglo-Saxon emigration has begun to pour down upon it, armed with the plough and the rifle, and marking its trail with schools and colleges, courts and representative halls, mills and meeting-houses.
O'Sullivan sees the future realm of the United States as a land marked by the advancement of Anglo-Saxons. This advancement will be attained by both the "plough," referring to agricultural techniques, and the "rifle," referring to the ability of the U.S. army to kill those who stand in their way. It will be a place of education, law, business, and self-government, according to O'Sullivan.
O'Sullivan believes the settlers in California 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." That is, he believes that these settlers have won their right to self-government by constructing homes in the "wilderness." However, the land these settlers took over was in some places owned by settlers from Mexico or Native Americans, something that O'Sullivan ignores. He also predicts the future of the West will be tied with that of the rest of the nation through the railroad and the telegraph. In short, he predicts that the West will soon be controlled by Americans, which happened after the Mexican-American War.
John L. O'Sullivan is largely credited with coining the term "Manifest Destiny.O'Sullivan, editor of The Democratic Review and ardent supporter of the Democratic Party supported the annexation of Oregon and Texas territory in an article in which he stated:
Our manifest destiny is to overspread the continent allotted by Providence for the free development of our yearly multiplying millions.
In a second article, published on December 27, 1845, he wrote:
And that claim is by the right of our manifest destiny to overspread and to possess the whole of the continent which Providence has given us for the development of the great experiment of liberty and federated self-government entrusted to us.
To O'Sullivan, God had given the whole of North America to the American people as something of a "promised land," in return for which they were responsible for spreading Republican style democracy. O'Sullivan saw the destiny of the United States as something of a moral, or "higher law;" so much so that it transcended International Law. Even so, O'Sullivan did not support military intervention. He believed that since this was the manifest destiny of the people of the United States, it would happen inevitably with the immigration of Anglo-Saxon Americans to other areas--the culture would follow the people. Interestingly, he opposed the Mexican War, although he later stated that the result was beneficial to both the U.S. and Mexico.
I assume that you are referring to John L. O'Sullivan's article "The Great Nation of Futurity." There, O'Sullivan describes what he sees as the destiny of the United States. In the article, O'Sullivan's vision is that America will create on Earth the most perfect society possible. He argues that it will
... establish on earth the noblest temple ever dedicated to the worship of the Most High -- the Sacred and the True.
To O'Sullivan, this would involved territorial expansion. He said that the floor of the US's "temple" would be a hemisphere and the roof would be the sky. But this is not the main point he is trying to make. What he is saying is that the future United States will be a place that is holy, one whose ways are based on the dictates of God.
O'Sullivan, then, believes the future US will bring God's will to earth by establishing freedom and liberty in its (expanding) territory.