Of the major worldwide powers in the philately era (that is, since 1840), the least imperialistic has been the United States. Great Britain and France had between them hundreds of imperial philatelic entities. Germany was a big player, and even Italy, which had more of an appetite for conquest than the digestion, had fifty or more imperial philatelic areas for which she issued stamps. Partly because our own internal markets were so large, partly because of immigration, partly because of endless land to be developed, and maybe a bit because of our democratic aspirations, America was a far smaller player in the Imperial game than our European competitors.
This changed a bit in the late Nineteenth Century when the Spanish American war gave America three colonies