|Percy Bysshe Shelley
I found evidence for his claims in a play published in 1820, Prometheus Unbound, by the English poet Shelley, who, sure enough, thought that in a reformed society man would be "uncircumscribed", the "king over himself" and therefore "tribeless and nationless".
There is more evidence that the liberal "intellectual and philosophical brew" (as one of my readers put it in the comments) was already well and truly set in place by the 1820s and that is Shelley's attitude to sex distinctions (Shelley identified as a liberal, collaborating with Byron and Hunt in 1822 to produce a literary periodical titled the Liberal).
It was not only nationality that Shelley wanted erased, but also distinctions between men and women. That makes sense from the liberal point of view. If the idea is to be unconstrained in your will as an individual, then our inherited, biological sex will be thought of negatively as something unchosen and predetermined. It then makes sense for liberals to want to make it no longer matter.
"these detestable distinctions will surely be abolished in a future state of being" 
Nor was Shelley alone in the literary and political current he belonged to in holding such a view. Shelley would later marry the daughter of the early feminist Mary Wollstonecraft. In 1792 Wollstonecraft had written:
A wild wish has just flown from my heart to my head, and I will not stifle it, though it may excite a horse-laugh. I do earnestly wish to see the distinction of sex confounded in society
You can find the same view in the writings of other early feminists. For instance, the American feminist Sarah Grimke wrote in 1837:
permit me to offer for your consideration, some views relative to the social intercourse of the sexes. Nearly the whole of this intercourse is...derogatory to man and woman...We approach each other, and mingle with each other, under the constant pressure of a feeling that we are of different sexes...the mind is fettered by the idea which is early and industriously infused into it, that we must never forget the distinction between male and female...Nothing, I believe, has tended more to destroy the true dignity of woman, than the fact that she is approached by man in the character of a female.
... Until our intercourse is purified by the forgetfulness of sex...we never can derive that benefit from each other's society...
Unsurprisingly, Shelley (despite marrying twice) was also in principle opposed to marriage. Again, if the aim is to be subject only to your own will, then it becomes difficult to accept the ideal of a commitment to a lifelong, exclusive union. In the same letter to Elizabeth Hitchener quoted above, Shelley writes:
Miss Weeke's marriage induces you to think marriage an evil. I think it an evil - an evil of immense and extensive magnitude...Marriage is monopolizing, exclusive, jealous.
(Interesting that Shelley makes some sort of appeal to an ideal of inclusiveness here.)
In the next post I intend to look a little deeper into the development of the words "liberal" and "liberalism" as I believe this sheds some light on how literary figures like Shelley and Byron ended up with their world view.
 Letter to Elizabeth Hitchener, 26th November 1811, p.119 here.
A note to Melbourne readers. If you are sympathetic to the ideas of this website, please visit the site of the Melbourne Traditionalists. It's important that traditionalists don't remain isolated from each other; our group provides a great opportunity for traditionalists to meet up and connect. Details at the website.