Washington even referred to the new Nation as an Empire in that speech. Here is the paragraph:
The Citizens of America, placed in the most enviable condition, as the sole Lords and Proprietors of a vast tract of Continent, comprehending all the various Soils and Climates of the World and abounding with all the necessaries and conveniences of life, are now, by the late satisfactory pacification, acknowledged to be possessed of absolute freedom and Independancy—They are from this period to be considered as the Actors, on a most conspicuous Theatre, which seems to be peculiarly designated by Providence for the display of human greatness and felicity, here they are not only surrounded with every thing which can contribute to the completion of private and domestic enjoyment, but Heaven has crowned all its other blessings by giving a fairer opportunity for political happiness, than any other Nation has ever been favored with—Nothing can illustrate these observations more forcibly than a recollection of the happy conjuncture of times and circumstances under which our Republic assumed its Rank among the Nations—the foundation of our
Empire was not laid in the gloomy Age of ignorance and superstition, but at an Epocha when the rights of Mankind were better understood and more clearly defined, than at any former period—The researches of the human Mind after social happiness have been carried to a great extent, the treasures of knowledge acquired by the labours of Philosophers, Sages and Legislators, through a long succession of years, are laid open for our use and their collected wisdom may be happily applied in the establishment of our forms of Government. The free cultivation of letters, the unbounded extension of Commerce, the progressive Refinement of manners, the growing liberality of sentiment, and, above all, the pure and benign light of Revelation, have had a meliorating influence on Mankind and encreased the blessings of Society. At this Auspicious period the United States came into existence as a Nation, and if their Citizens should not be completely free & happy, the fault will be entirely their own.
From George Washington to The States, 8 June 1783
founders.archives.gov