It is very much a twist on Adam Smith’s argument about the division of labor:
One further remark however, which I cannot omit, is that the people in America are necessitated, by their local situation, to be more sensible and discerning, than nations which are limited in territory and confined to the arts of manufacture. In a populous country, where arts are carried to great perfection, the mechanics are, obliged to labour constantly upon a single article. Every art has its several branches, one of which employs a man all his life. A man who makes heads of pins or springs of watches, spends his days in that manufacture and never looks beyond it. This manner of fabricating things for the use and convenience of life is the means of perfecting the arts; but it cramps the human mind, by confining all its faculties to a point. In countries thinly inhabited, or where people live principally by agriculture, as in America, every man is in some measure an artist— he makes a variety of utensiles, rough indeed, but such as will answer his purposes— he is a husbandman in summer and a mechanic in winter— he travels about the country— he convenes with a variety of professions— he reads public papers— he has access to a parish library and thus becomes acquainted with history and politics, and every man in New England is a theologian. This will always be the case in America, so long as their is a vast tract of fertile land to be cultivated, which will occasion emigration from the states already settled. Knowledge is diffused and genius routed by the very situation of America.
That is from his Sketches of American Policy, #29.