Saul Bellow, More Die of Heartbreak
Hitchings explains that at the time of Beverley's writing the word American was already in use, but it was used to describe Indians, not colonists. Up until the Revolution, most colonists still thought of themselves as British or as Virginians or Pennsylvanians or whatever, depending on which colony they happened to live in. And apparently some of them considered themselves Indians, living as they did on a continent populated with Indians.
The narrator of Saul Bellow's novel More Die of Heartbreak seems to think what you call yourself is just a matter of choice and, of course, residency. For a Parisian to become a New Yorker, he just has to move to New York City. Yet it may not be that simple, especially if one is talking about a country, not a city. There is the question of citizenship, for example. There are also the questions of language, culture, length of residency and, of course, how you are accepted by other people in that country.
Just three pages later in Bellow's novel, his narrator writes about moving to a Midwestern city to teach at a university, after spending most of his life as an American in Paris. "Arriving, I felt conspicuously foreign. But in fact Iranians are driving the taxis, Koreans and Syrians own the vegetable markets. Mexicans wait on tables, an Egyptian services my television set, Japanese students take my Russian course." In other words, this American by way of France, despite what he said earlier, thinks of many of his fellow residents of that city according to their country of origin, not according to where they are currently living or even what their citizenship may be.
Even today, no less than in the 18th century, it takes some time to become fully American.