On 10 August, after days of intense fighting, secessionist forces of the Southern Transitional Council in Yemen seized control of Aden, deposing the internationally recognised government of President Abdrabbuh Mansur Hadi. The STC and the Hadi government are nominally allies in the war against the Houthis. The two senior partners in the war’s disintegrating coalition, Saudi Arabia and the UAE, also found themselves on opposite sides in the battle for Aden. The Saudis strongly favour the Hadi government; the Emiratis have long-standing ties with the STC.

The Saudi-led coalition formed in March 2015, after Houthi forces from Yemen’s north-west expelled Hadi from the capital, Sana’a. But the shared goal of beating back the Houthis masked serious internal contradictions. Hadi’s commitment to national reunification under his restored presidency was incompatible with the secessionists’ agenda, and the government’s relations with a local Muslim Brotherhood affiliate were of concern to the UAE and its allies on the ground. The Saudis meanwhile, though also ill-disposed to the Islamists, were more worried by the Houthis and their (overstated) ties to Iran, and for that reason backed an increasingly isolated Hadi.

The divisions were exacerbated by a new split at the top of the coalition. The UAE recently announced a major draw down of its military presence in Yemen, after apparently coming to the conclusion – not shared by the Saudis – that the continued pursuit of battlefield victory was futile. These developments have left the war against the Houthis in tatters. One of the two senior partners in the coalition has effectively given up; the Yemeni component of the coalition has fallen apart; and the Hadi government, whose restoration was the coalition’s official war aim, has been kicked out of a major city for a second time in five years. Hadi himself has long been resident in Saudi Arabia, and the chances of his returning as president of a unified Yemen are fanciful at this point.

The Yemeni people have paid the costs of the Gulf monarchs’ folly. Around 100,000 are thought to have met a violent death since the war began, and the blockade imposed by the Saudis and their allies is the main cause of the world’s worst humanitarian crisis. Millions are on the brink of famine. According to Save the Children, as many as 85,000 infants have died from starvation or preventable disease.

Aerial bombing by the Saudis is responsible for most of the violent civilian deaths. Bombs supplied by Britain and America are dropped from planes built by Britain and America, flown by pilots trained by Britain and America, and kept in the sky with British and American maintenance. The humanitarian cost is indescribable and the war clearly unwinnable. The purpose of continuing British and American support can only be to spare the blushes of the Saudi crown prince Mohammed Bin Salman, in whom London and Washington have invested so much, and who apparently started the intervention thinking it would be over in a few months.

In the US, pressure is mounting in Congress to force the Trump administration to pull the plug on Bin Salman’s war. In the UK, the pressure is coming from the courts. Arms sales are illegal if there is a clear risk the weapons might be used in serious violation of international law, and in June the Court of Appeal ruled that the government had acted unlawfully by failing to assess properly the risk of continuing to arm the Saudis. In fact the government hadn’t carried out any formal assessment of alleged Saudi violations, presumably because it knew full well what conclusion any credible assessment would have reached.

The court ordered that no new arms export licences be granted and all existing licences be reviewed. The government plans to appeal but the ground is shrinking beneath it. A new, detailed report compiled by a Yemeni human rights group documents numerous instances of the Saudi-led coalition targeting civilians and civilian infrastructure, and then whitewashing the evidence. The Saudis’ assurances of their own good behaviour and sincere wish to adhere to international law are cited by Whitehall in support of its cynical and self-serving decisions on arms export licensing.

It recently emerged that UN experts had reported in January 2018 discovering fragments of British-made laser-guided bomb parts at the site of a September 2016 airstrike that breached international law. Over the course of four and a half years of indiscriminate bombing, Britain has enabled a pattern of international law violations by the Saudis. The fact that arms exports have continued regardless is proof that the legal controls on their sale are worthless.

The US government knew by the mid-1960s that the Vietnam War was unwinnable, admitting internally that the primary objective was to avoid humiliation. Testifying before a Congressional committee in 1971, the young Vietnam veteran John Kerry asked senators: ‘How do you ask a man to be the last man to die for a mistake?’ Kerry was US secretary of state for the first 22 months of the Saudi-led intervention in Yemen, through some of the Kingdom’s worst atrocities. The Saudi war on Yemen, like the US war on Vietnam, has been criminal as well as mistaken. We may never know who the last person to die as a result of it will be.