Arguments in favour of the legalisation of torture have not lost their capacity to shock. The fact that US attorneys-general and the senior legal adviser at the state department have said they are in favour of it seems proof to many of America's slide into barbarism. In reality, however, their pro-torture arguments are no different from the claims made in favour of "humanitarian war" and of other forms of military intervention - arguments that, unfortunately, have become increasingly popular since the end of the cold war.

Torture and "humanitarian war" are similar in many ways. Both involve the inflicting of violence in order to force a change of behaviour. Both are predicated on the assumption of guilt: torture is justified because the victim is said to be a terrorist, or an "illegal combatant" who has committed or is about to commit a terrible crime, while pre-emptive war is justified because a state is said to be "a rogue state" violating international law (Iraq) or committing crimes against humanity (Yugoslavia). It is therefore no coincidence that the US administration that justifies its wars in the name of claims about humanity and its right to liberty also advocates the use of torture to protect these.

Torture and war have been the subject of absolute or near-absolute interdiction in international law. In the aftermath of the second world war, the Nuremberg and Tokyo trials established the principle that crimes against peace are the supreme crime. Aggressive war "contains within itself the accumulated evil of the whole", said the Nuremberg judges, who understood that once war starts, war crimes will inevitably follow. It was therefore better to ban it completely. This was done by the UN charter, which declared all war, including so-called humanitarian war, illegal. War is allowed only in the very restricted and clear-cut cases of self-defence and when authorised by the security council. Torture was similarly banned by UN convention in 1985.

Any attempt to legalise torture or war was simply regarded as the thin end of the wedge. Today, however, many people who say they shudder at the abuses committed by the Spanish Inquisition, or by the Americans at Guantánamo, campaign actively in favour of war. Humanitarian intervention became fashionable as soon as Iraq was bombed in 1991 "to protect the Kurds and the Shia". Now the trump question put to anti-interventionists is: "What would you have done about Rwanda?" Yet this is the same argument as that advocated by the torturer who says he is trying to save lives. Activists in favour of international judicial and military intervention denounce peacemaking and amnesty laws as acts of appeasement, and they typically strive to break down antiwar sentiment by getting people to admit that intervention might be justified in some extreme cases. But if it is, then why not torture too?

This unwelcome campaign to give war a chance persists in spite of the fact that the very abuses that inspired the universal ban on war in 1945 have indeed been committed by the Americans and their allies in their assault on the old postwar sovereignty-based system of the UN charter. There were no weapons of mass destruction in Iraq and there was no genocide in Kosovo (Milosevic was never charged with it), but many people still regard war as something at least potentially civilised. We need instead to renew the deep conviction that seized the collective conscience of mankind in 1945 that the international system, and the ideas that underpin it, should be structured so as to ensure peace at any price.

· John Laughland's A History of Political Trials from Charles I to Saddam Hussein is published next May

jlaughland@btinternet.com