This was music to Kirchner's ears. She has marked the 30th anniversary of the Argentine invasion - and British recapture of the island group - with a high-profile, nationalist campaign to "recover" the Falklands (or Las Malvinas, as Argentines call them).

Penn then went home to California, but Fidel Castro soon weighed in too. Unfortunately, Castro hadn't read the script.

Kirchner's chief point was to accuse Britain of "militarising" the South Atlantic by sending an "ultra-modern destroyer" to patrol the waters around the islands (to replace an obsolete, leaky destroyer, we must suppose). Castro unhelpfully mocked the British, claiming: "the English only have one little boat left.

"All the English can do is send over a destroyer, they can't even send an aircraft carrier."

One could make a meal of this silly quarrel - "The Falklands thing was a fight between two bald men over a comb," as Argentine poet Jorge Luis Borges once said - but a more useful approach would be to consider why it is so fundamentally silly.

It's not the silly history of rival claims over the Falklands: first French in 1764, then British in 1765, then the French handed their share to the Spanish in 1767, followed by half a dozen more changes of ownership or control - until the islands fell under permanent British rule in 1833. Nor is it that the islands' seabed oil and rich fisheries are now worth considerably more than a comb.

It's just that you are no longer allowed to shift control of territories from one country to another by force. After World War II the nations of the world in effect froze all the borders where they were at that moment - because most wars were over territory, and had got too big and destructive to fight any longer.

This is the point at which frantic protests about British "colonialism" usually erupt from Argentina, where the European settlers dispossessed the aboriginal inhabitants. And from Sean Penn, whose house sits on land that was part of Mexico until the US conquered it in 1846.

But the line was actually drawn in 1945 and has proved remarkably robust. African countries got their independence within the borders originally drawn by the imperial powers, with little heed to ethnic realities. When the old Soviet Union fell apart, all 15 successor states accepted the administrative divisions of that empire as their new borders.

And whenever somebody tried to change their borders by force, they were firmly rebuffed by almost everybody else.

Indonesia seized and annexed East Timor in 1975, but eventually had to give it its freedom. Saddam Hussein's Iraq invaded and annexed Kuwait in 1990, but was driven out by an international army after only a few months.

And Argentina invaded the Falklands in 1982.

It was driven out by the British, who would never have fought such a difficult war if it had not had international law on its side.

As for Kashmir and the West Bank, that's a subject for another day.

Gwynne Dyer is a London-based independent journalist whose articles are published in 45 countries.