Leading article: Another skittle of the old order falls

That is that. The end. This time, it is the end for John Howard. It is all over for another leader identified with the invasion of Iraq. Jose Maria Aznar of Spain was voted out in 2004; Silvio Berlusconi of Italy fell last year; Tony Blair was forced out by his own party earlier this year; Jaroslaw Kaczynski of Poland lost last month; only George Bush, the prime mover, is left, and as he sets records for unpopularity he is a much reduced figure, limping to his expiry date in 2009.

Mr Howard, the four-time winner, has finally been defeated, with the added humiliation of almost certainly losing his own seat. Australia has for the first time anywhere in the world – one of those rare facts not easily checked on Google – a prime minister called Kevin.

We do not want to ascribe too much importance to Iraq. It was not the dominant issue of the election campaign. Mr Howard has, like Mr Bush and Mr Blair, been re-elected once since the Iraq war. And in Britain and the US, the new faces do not represent an unequivocal repudiation of past policy. Gordon Brown has rebalanced our Government's rhetoric in a welcome fashion, but he is bound by the collective decision to join the invasion. The front-runner to succeed Mr Bush, Hillary Clinton, is equally bound by her support for it at the time; the war's most clearly defined opponent, Barack Obama, has a long way to go to win the Democratic nomination, let alone the presidency.

However, Mr Howard's defeat in Australia is undoubtedly part of the slow unwinding of the failed worldview that was the mistaken response to the horror of 9/11. As the leaders who promulgated that view leave the stage, the world has the chance to rebalance both the rhetoric and the rules.

We should make it clear that this newspaper, despite its opposition to the Iraq invasion, does not repudiate the idea of liberal interventionism altogether. We do not argue that nations should never interfere in the internal affairs of other sovereign nations. Nor must every intervention have the explicit approval of the Security Council.

We hold to the position of the late Robin Cook, Foreign Secretary in Mr Blair's first term. He oversaw the use of military force against Serbia over Kosovo. UN authorisation was never sought, because it was known that Russia and China would use their vetoes. But the action did have the united support of the 19 member states of Nato, and the legal basis in preventing crimes against humanity.

The Independent on Sunday supported intervention in Afghanistan. One reason for our campaign to renew the military covenant – joined last week by six retired top brass in the Lords – is that we believe the mission there requires a long-term and deep commitment.

We appreciate that, if the UN is not the absolute arbiter, it is harder to draw hard and fast rules. We accept that liberal interventionism becomes a matter for pragmatic judgement. But there are principles against which that judgement can be exercised.

Last week, Jonathan Powell, Mr Blair's former chief of staff, set out his view: "We should have been clear we were removing Saddam because he was a ruthless dictator [but] there was no legal basis for proceeding on these grounds, and so we were not able to make this case as wholeheartedly as I would have liked."

That would have been just as inadequate as the flawed case that Mr Blair made. But we do not think it wrong in principle. If we can prevent barbarism, we should consider it. We think Mr Blair was right to ask Charles Guthrie, the Chief of the Defence Staff, to "look at" the feasibility of military action in Zimbabwe, as we revealed this month. He was right to canvass the possibility of military action in Darfur. He was right to decide against deploying troops in both places, and he should have said the same about Iraq.

If stringent tests are met, Britain should be prepared to take part in military action around the world. The tests are similar to those set out by Mr Blair in his Chicago speech in 1999 during the Kosovo conflict: the action must avert crimes against humanity, it must command wide international support, and it must be reasonably certain of success. None was satisfied in Iraq; all were satisfied in Afghanistan.

Now those tests must be applied to new challenges – or, rather, to old challenges faced anew. In Kosovo, as Melanie McDonagh argues today, we need once again to decide the right mix of military and diplomatic response. And, as the leaders of the Middle East gather in Annapolis, Maryland, we need to decide how much other countries should contribute to peacekeeping in Palestine.

Increasingly, such decisions can be taken by leaders who no longer have to defend the bad decisions of the past. As each skittle falls, our confidence grows that a better form of liberal interventionism will prevail.