Donald Trump’s threat to destroy the sites of ancient Persia should send a shiver down the spine of any civilised person. How can anything justify American bombing of Persepolis or the mosques of Isfahan? Only the demented can see them as “threatening America”. It is on the same ethical plane as the Islamic State vandalism of Palmyra and Mosul.

The destruction of cultural artefacts in war is specifically outlawed under the Hague convention of 1954 and subsequent protocols. It ranks with genocide, chemical weapons and the “strategic” bombing of civilians as beyond the pale of human behaviour. The US does not recognise most of these treaties as it concedes extraterritorial sovereignty, but it normally obeys them.

What is clear is that modern weaponry is making a mockery of the legality – let alone the ethics – of war. The drone has turned an onscreen war game into reality. Its invulnerability has raised it beyond the realm of international law. The drone is its own ethicist. Even Barack Obama caught the bug in 2011, justifying a drone assassination in Yemen despite national and international laws and conventions. British governments have behaved likewise. Superpowers don’t obey laws, they make them.

The assassination of leaders has long been seen as senseless, if only for inviting violent retaliation. The drone has merely raised the stakes of such tit-for-tat escalation. Reports from Washington suggest military officials didn’t seriously think Trump would take the most extreme option of those presented to him, in killing Qassem Suleimani as a response to what was believed to be Iranian-prompted violence in Iraq. The president ordered the action, as might Genghis Khan, in a fit of pique after an attack on the US’s Baghdad embassy. The famed checks and balances in the American constitution are clearly ineffective.

Retaliation against sites termed by Trump as “important to Iran & the Iranian culture” is a new escalation. Few hands are clean in this area of conflict. Britain’s terrorist bombing by the RAF against Germany in the second world war was blatantly aimed at historic towns. Arthur “Bomber” Harris, the head of RAF Bomber Command, held that destroying Germany’s heritage would break the enemy’s spirit and force it to surrender. That he – and Winston Churchill – thought bombing Lubeck, Nuremberg and Dresden would somehow persuade Adolf Hitler of the error of his ways shows only that war drives men insane. Hitler merely retaliated with the Baedeker raids on English cathedral cities.

Harris is born again in Trump. Nothing could be more calculated to bond Iranians to their leaders – and demand revenge – than the destruction of their history. Policy should be aimed at precisely the reverse, creating conditions in which opposition to the military/clerical regime can prosper and strengthen. Bombing Persepolis would not only be grotesque, it would be utterly counterproductive. It is the act of a belligerent personality craving war.

• Simon Jenkins is a Guardian columnist