It's not a "21st century invention," not even because it has a longer history than that, but because it's just marriage. It isn't an innovation. Any more than women's suffrage was an innovation. In both cases it's extending enfranchisement to more people.
> At the same time, many of these relationships might be more clearly understood as mentoring relationships between adult men and young boys rather than an analog of marriage.
Of the western world it says:
> Conubium existed only between a civis Romanus and a civis Romana (that is, between a male Roman citizen and a female Roman citizen), so that a marriage between two Roman males (or with a slave, amasius) would have no legal standing in Roman law (apart, presumably, from the arbitrary will of the emperor in the two aforementioned cases)
Of China:
> While the relationship was clearly approved by the wider community, and was compared to heterosexual marriage, it did not involve a religious ceremony binding the couple.
Of early modern times:
> Michel de Montaigne, a 16th-century French philosopher and prominent essayist, reports having heard a third-party description of a same-sex wedding occurring some years earlier using the usual Tridentine marriage ceremonies of the Roman Catholic Church. The ceremony was said to have occurred a few years before 1581, at the San Giovanni a Porta Latina basilica in Rome and the participants were burned at the stake by the Vatican
It then claims Anne Lister married Ann Walker, but if you read the article detailing this marriage, there wasn't any sanctioned ceremony. Rather the two women took communion together and thereafter they considered themselves married. There was no socially sanctioned recognition: https://en.wikipedia.org/wiki/Anne_Lister#Relationship_with_...
> Eventually the women took communion together on Easter Sunday (30 March) 1834 in Holy Trinity Church, Goodramgate, York, and thereafter considered themselves married, but without legal recognition.
It literally says all this in your article. Did you read it?
The only references to pre-modern homosexual marriage are hearsay reports of Siwa oasis and the Phillipines. Neither of these cite written records or any sort of proof, and both of these would have been in somewhat literate societies.