I consider rightful claims to land to be based on usage of unused land
I agree with this, as I have since you first mentioned it. Using this definition of a valid claim, Britain had at least some claim to at least part of the island earlier than Spain, to say nothing of Argentina. By continuously occupying and using the land from 1766-1780, they originally co-existed with the French, then co-existed with the Spanish for several more years. That's a valid claim, at least to part of the island. Britain didn't displace anyone, their neighbors generally didn't contest British claims, and Britain used the land.
They only stopped using the island in 1780, when the Spanish forcibly evicted them. That's not a valid termination of the British claim -- you can't just conquer someone's land and say they no longer have rights to it. And as soon as the Spanish left in 1811, British users came right back in, and seem to have continuously used the island up through when the British military returned in 1833. In short, there has been continuous British use of the island since 1766, with the only exception being when Spain (wrongly) conquered and occupied their part.
As for trading land and the French-Spanish swap early on, I think trading land is fine so long as the recipient uses it, which Spain (at least initially) did. However, when Spain abandoned the island -- pulling out every Spanish occupant -- never returned, and never re-asserted its claim, I see no reason to honor that claim any longer. Similarly, I see no reason to say that claim was transferred to Argentina: it wasn't traded, and it wasn't won in an independence struggle. Any argument in the form of "well it was part of the Vicereoyalty of Rio de la Plata, too" falls apart too, because the whole Viceroyalty didn't initially rebel (see Paraguay), and what was to become Argentina never really had control/use/occupation of the entirety of the part that did rebel (Bolivia and Uruguay soon split off, and much of the "desert" outside of Buenos Aires was indigenous-controlled and would be for decades). Certainly Argentina can't just claim any territory once claimed by Spain -- again, it comes back to what Argentina was actually using, with the corollary that you can't just show up on someone else's land and kick them out.
In reality, the way claims operated in the time these claims were made
I'm not putting much stock in these for two reasons. First, as leftists and anti-imperialists I would imagine we're both rightly critical of the Pope dividing up lands a continent away (nearly all of which Europeans had never seen, much less visited or used) for colonial powers. Second, as you point out, the only real rule was who could get away with holding a piece of land, and the rest was legal fictions largely invented after the fact as justification. That's not a good standard, but Britain would clearly win under it, too.
Before that, the British desire for the islands was purely geopolitical posturing.
British sealers were using the island for commercial purposes since at least 1776, and probably earlier. They didn't just set up a garrison and hang out. Britain certainly wasn't posturing any more than any other involved power was.
Spain had the best claim because it was transferred back to them through sale.
At most, this was a claim to part of the island, while the British had a valid claim to another part of the island. The British and French were co-existing in the Falklands before the French port was sold to Spain.
As Argentina was the only remaining nation who had done any development on the island administering it on behalf of Spain
I don't know if the Viceroyalty of Rio de la Plata -- a Spanish colony -- did much administering of the island. Even if we say that there was significant administration (not use) by the Viceroyalty, and even if we want to give Argentina credit for what its predecessor colony did, there's still the matter of Spain totally abandoning the Falklands in 1811, and the matter of Britain having at very least a partial claim to the island from the 1700s.
Britain again only became interested because they saw Argentina moving in to develop the area
But use is the touchstone here, not intentions. And Britain used the island consistently as a port for sealers during the whole time in question, excepting when they had been forced out by Spain.
It was several more decades before they developed it as anything besides corporate holdings. I
It wasn't just a holding, it was being used. Use of the land is what determines a valid claim, right?
The economic pressures on an island requiring external supply to be at all viable is such a coercive force that I don’t think a true claim of self-determination was ultimately possible for that populace.
I completely disagree with writing off claims of self-determination on the grounds that you buy things from elsewhere. I'm not sure it's accurate to say an external supply is "required," anyway -- like most places, they've undoubtedly structured their economy not around self-sufficiency, but around profitability, so what they're currently doing isn't a reflection of what they're capable of.
deleted by creator
I agree with this, as I have since you first mentioned it. Using this definition of a valid claim, Britain had at least some claim to at least part of the island earlier than Spain, to say nothing of Argentina. By continuously occupying and using the land from 1766-1780, they originally co-existed with the French, then co-existed with the Spanish for several more years. That's a valid claim, at least to part of the island. Britain didn't displace anyone, their neighbors generally didn't contest British claims, and Britain used the land.
They only stopped using the island in 1780, when the Spanish forcibly evicted them. That's not a valid termination of the British claim -- you can't just conquer someone's land and say they no longer have rights to it. And as soon as the Spanish left in 1811, British users came right back in, and seem to have continuously used the island up through when the British military returned in 1833. In short, there has been continuous British use of the island since 1766, with the only exception being when Spain (wrongly) conquered and occupied their part.
As for trading land and the French-Spanish swap early on, I think trading land is fine so long as the recipient uses it, which Spain (at least initially) did. However, when Spain abandoned the island -- pulling out every Spanish occupant -- never returned, and never re-asserted its claim, I see no reason to honor that claim any longer. Similarly, I see no reason to say that claim was transferred to Argentina: it wasn't traded, and it wasn't won in an independence struggle. Any argument in the form of "well it was part of the Vicereoyalty of Rio de la Plata, too" falls apart too, because the whole Viceroyalty didn't initially rebel (see Paraguay), and what was to become Argentina never really had control/use/occupation of the entirety of the part that did rebel (Bolivia and Uruguay soon split off, and much of the "desert" outside of Buenos Aires was indigenous-controlled and would be for decades). Certainly Argentina can't just claim any territory once claimed by Spain -- again, it comes back to what Argentina was actually using, with the corollary that you can't just show up on someone else's land and kick them out.
I'm not putting much stock in these for two reasons. First, as leftists and anti-imperialists I would imagine we're both rightly critical of the Pope dividing up lands a continent away (nearly all of which Europeans had never seen, much less visited or used) for colonial powers. Second, as you point out, the only real rule was who could get away with holding a piece of land, and the rest was legal fictions largely invented after the fact as justification. That's not a good standard, but Britain would clearly win under it, too.
deleted by creator
British sealers were using the island for commercial purposes since at least 1776, and probably earlier. They didn't just set up a garrison and hang out. Britain certainly wasn't posturing any more than any other involved power was.
At most, this was a claim to part of the island, while the British had a valid claim to another part of the island. The British and French were co-existing in the Falklands before the French port was sold to Spain.
I don't know if the Viceroyalty of Rio de la Plata -- a Spanish colony -- did much administering of the island. Even if we say that there was significant administration (not use) by the Viceroyalty, and even if we want to give Argentina credit for what its predecessor colony did, there's still the matter of Spain totally abandoning the Falklands in 1811, and the matter of Britain having at very least a partial claim to the island from the 1700s.
But use is the touchstone here, not intentions. And Britain used the island consistently as a port for sealers during the whole time in question, excepting when they had been forced out by Spain.
It wasn't just a holding, it was being used. Use of the land is what determines a valid claim, right?
I completely disagree with writing off claims of self-determination on the grounds that you buy things from elsewhere. I'm not sure it's accurate to say an external supply is "required," anyway -- like most places, they've undoubtedly structured their economy not around self-sufficiency, but around profitability, so what they're currently doing isn't a reflection of what they're capable of.