It's not a very good phrase, since "greatest" means whatever the speaker wants it to mean. You could plausibly say that about almost any country - everyone has

It's not a very good phrase, since "greatest" means whatever the speaker wants it to mean. You could plausibly say that about almost any country - everyone has something they're "the greatest" at. To be fair, though, I reckon that there was a period in time in which the USA did seem to be holding the generally accepted global flag for "the country that's doing things right". Not perfect, but the USA had a much better reputation than it does now for generally having its shit together and moving in the right direction. Cracks started to appear in the 1970s, I'd say, and the edifice had completely crumbled by the mid 90s.