Our Founding Fathers knew the great risk (hence the Great Experiment) they were undertaking; a massive republic, by historical standards, in the form of a republican confederation. Would it stand the test of time, which no other republic had? This is the underpinning they knew had to exist, and exactly why they exhorted the absolute need for a Christian foundation of virtue, righteousness, and justice. No other means could hold together a republic, let alone a large Union of republics. It would need God’s Providence and to be modeled after the only God-sanctioned structure; that of the Ancient Hebrews.
Alexis de Tocqueville repeatedly throughout Democracy in America recognized America as a republican confederation of separate sovereign nation-States, noting that, “Each of the States which compose the Union” form this confederation. “This spirit of amelioration is constantly alive in the American republics,” he continues, “without compromising their tranquility…of the republican form of government.” Here Tocqueville, as he does throughout his dissertation, refers to each separate republic as a “State,” meaning a separate sovereign nation-States which each itself is under a republican government. Together they formed into a “Union” – or a voluntary and Compact-formed confederation of nation-States, also under a republican form of government.
On January 18, 1800, James Madison wrote to Thomas Jefferson. In the letter Madison discloses his thoughts on the source principle on which the Americans declared and fought for their independence. It would correlate with the American Compact which had created a confederacy, or Union as our Founders would often reference. Madison divulges that, “The fundamental principle of the Revolution was, that the Colonies were co-ordinate members of with each other.” He would then compare and contrast the American Union, or collection of separate and sovereign nation-states, with the single nation-state of England. Madison continues, “with Great Britain, of an empire united by common executive sovereign, but not united by any common legislative sovereign. The legislative power was maintained to be as complete in each American Parliament, as in the British Parliament…A denial of these principles by Great Britain, and the assertion of them by America, produced the Revolution.” 
It is why Bishop James Madison, President James Madison’s cousin, in a sermon in 1795 pronounced “that virtue is the vital principle of a republic” and “that virtue is the soul of a republic.” Bishop Madison continues by declaring that this virtue will not manifest “without religion, I mean rational religion, the religion which our Saviour himself delivered,” a country would not have “real virtue and social happiness.”
Another reason for the limited government at the federal level was to keep power as close to the people as possible and to maintain sovereignty of the States. That is why we are called the United States. This allows for the freedom for each state to experiment within the Great Experiment with particular economic, social, and governance issues in the manner they see fit and to serve the interests of the citizens of each State. Fifty sovereign countries united, but free to evolve and develop practices which other states can adopt and modify to suit their needs. This has allowed the greatest prosperity and knowledge development in the history of the world.
Founding Father and arguably one of the major spearheads of the American Revolution, Samuel Adams, wrote in 1771 in the Boston Gazette under the pseudonym Valerius Poplicola, that individual colonies were “a separate body politick.” Adams continued noting that the colonists had “a right equal to that of the people of Great Britain to make laws for themselves, and are no more than they, subject to the control of any legislature but their own.” And referencing the great theologian Richard Hooker, Adams affirmed that, “The lawful of making laws to command the whole politick societies of men, belongs so properly unto the same intire societies, that for any prince or potentate of what kind soever upon earth to exercise the same of himself, and not by express commission immediately and personally receiv’d from God, or else from authority deriv’d at the first from their consent, upon whose persons they impose laws, is no better than mere tyranny.”
A very insightful description of the American compactual-republic was given in an 1896 essay by William Graham Sumner, a professor of political and social science at Yale College (Yale University). Professor Sumner eloquently writes in his essay, The Fallacy of Territorial Extension, that, “The fathers of the Republic planned a confederation of free and peaceful industrial commonwealths, shielded by their geographical position from the jealousies, rivalries, and traditional policies of the Old World [European nation-States] and bringing all the resources of civilization to bear for the domestic happiness of the population only.” Indeed, this is a grand description for an environment for the American Dream to blossom and grow.
Alexis de Tocqueville, 2007 (originally published in 1835 and 1840), Democracy in America, Volumes 1 and 2, Unabridged, (Stilwell, KS: Digireads.com Publishing), p. 124.
James Madison, January 18, 1800, “Letter to Thomas Jefferson,” Gaillard Hunt (ed.), 1906, The Writings of James Madison, Vol. 6, 1790-1802, (New York, NY: G.P Putnam’s Sons), p. 373, [http://lf-oll.s3.amazonaws.com/titles/1941/1356.06_Bk.pdf]. Also referenced in Jack P. Greene, 2011, The Constitutional Origins of the American Revolution, (New York, NY: Cambridge University Press), pp. 187-188.
Bishop James Madison, February 19, 1795, “Manifestation of the Beneficence of Divine Providence Towards America,” from Ellis Sandoz, (Ed.), 1991, Political Sermons of the American Founding Era: 1730 – 1805, (Indianapolis, IN: Liberty Press), pp. 1319-1320.
Jack P. Greene, 2011, The Constitutional Origins of the American Revolution, (New York, NY: Cambridge University Press), p. 122.
Samuel Adams, October 28, 1771, “Valerius Poplicola to the Boston Gazette,” in Harry Alonzo Cushing (ed.), 1906, The Writings of Samuel Adams, Vol. II, 1770-1773, (New York, NY: G.P. Putnam’s Sons), p. 261. Also referenced in Jack P. Greene, 2011, The Constitutional Origins of the American Revolution, (New York, NY: Cambridge University Press), p. 122.
William Graham Sumner, Albert Galloway Keller (ed.), 1911, “The Fallacy of Territorial Extension (1896),” War and Other Essays, (New Haven, CT: Yale University Press), p. 291. Also referenced at William Graham Sumner, Albert Galloway Keller (ed.), 1911, “The Fallacy of Territorial Extension (1896),” War and Other Essays, (Indianapolis, IN: Liberty Fund), [http://lf-oll.s3.amazonaws.com/titles/345/Sumner_0255_EBk_v6.0.pdf], p. 138.