The U.S. Constitution created an empire. Although the evidence for this fact is overwhelming, it's revisionist history because of the ingrained concept, reinforced by centuries of teaching and repetition, that the government created was a republic or a federated republic. With the glorification of this central government and continual reiteration by its supporters of its "virtues," the Articles of Confederation have been shunted aside and treated as a shabby and weak form of government.
Indeed, the central government's overt form had voting for representatives and no emperor, but functionally and operationally it had centralized power and it had the potential to consolidate and grow that centralized power. The central government was over and above the states in the critical areas where the empire could grow. In practice, the Congress-Executive-Judiciary took the place of an emperor. The key question is not where the powers to make critical decisions lay in the new U.S. government as compared with other empires, but the scope of those powers.
Those powers were seen even before the Constitution went into effect by the Anti-Federalists, whose writings are available (here and here) as well as commentary on them, such as here, here, and here. In the latter article appears this: "They saw that the unlimited right of Congress to tax and establish an army would eventually lead to an empire both at home and abroad." How soon was "eventually"? My point is that "eventually" was right away. Once institutionalized via the Constitution, the government could and did immediately begin dominating the states. The government could at times use its powers nationally in reflection of particular interest groups, states, regions and causes. Justin Raimondo analyzes the War of 1812 in that context as a victory of the war party. He also writes
"The warhawks, led by John Calhoun, were motivated less by outrage over British harassment of American persons and commerce than by the emerging delusion of Manifest Destiny that energized the earliest advocates of an international American empire. "
Raimondo reminds us of the attack on Canada, which failed, the non-cooperation of state and local militias being one reason. This was no longer the case in the Mexican-American War (1846-1848). Raimondo writes
"The young republic was infected with the virus of imperialism at an early age, and it ate away at the central organs of the body politic. The carriers were the intelligentsia, the social climbers, the politicians-on-the-make — those who, ironically, wished to emulate the British by building an American version of the Empire."
My point is that this "young republic" was that in form only. On paper, insofar as the Constitution makes it legal or accepted, the government was an empire, needing only to write the blank checks to institutionalize itself and make itself a known force.
The Alien and Sedition Acts, the Louisiana Purchase, and the fugitive slave laws show the empire in action. In the latter,
"The Fugitive Slave Act of 1793 created the mechanism for recovering a fugitive slave, overruled any state laws giving sanctuary, made it a federal crime to assist an escaped slave, and allowed slave-catchers into every U.S. state and territory. As free states sought to undermine the federal law, the even more severe Fugitive Slave Act of 1850 was enacted."
Jefferson several times wrote of the "empire of liberty", such as here:
"...we should then have only to include the North in our confederacy, which would be of course in the first war, and we should have such an empire of liberty as she has never surveyed since the creation: & I am persuaded no constitution was ever before so well calculated as ours for extensive empire & self government." — Jefferson to James Madison, 27 April 1809"
The continent lay before the framers and Americans. Land lay before the framers and Americans. Untold riches and wealth in land beckoned. Land speculation was an American constant. Empire as a form of government was the chosen vehicle for expansion into these lands. Dreams of liberty also prevailed, and the framers thought that empire and liberty could co-exist. This illusion has never been shattered, not even by the bloodiest of all American wars. Today, we inherit the problem that empire and liberty, in the final analysis, cannot be reconciled. One or the other must prevail. An empire of liberty is an impossibility. A strong central government that claims powers over every facet of life cannot be controlled. It becomes the controller.
(Thanks to Jeff P. Zacher, Daniel Ajamian, and Daniel Pitrone for their helpful comments. Two recent books on the anti-federalists are Herbert J. Storing's What the Anti-Federalists Were For and Paul Boyer's The Original Counter-Argument. I have read neither one. Boyer paraphrases the anti-federalist essays in modern prose; a long sample is here.)