The civil war in Yemen, which has persisted for five years today, has produced a humanitarian crisis of the highest magnitude.

It has its roots in the Houthi takeover of Sanaa in 2014, which forced the resignation of President Abd-Rabbu Mansour Hadi.

Beginning in March 2015, a coalition of Gulf states led by Saudi Arabia staged a military campaign against the Houthis with the goal of restoring Hadi's government.

Since then, the US and the United Kingdom have sold arms and provided technical and logistical assistance to Saudi Arabia and the United Arab Emirates (UAE), both of which have conducted air raids on Yemeni soil.

Iran, in its turn, has sent advanced weapons and military advisers to the Houthis.

The proxy conflict shows no sign of abating, despite the efforts by the UN's Special Envoy to implement a lasting ceasefire.

Five years later, the US remains steadfastly committed to the Saudi-led coalition which has been accused, by a United Nations Commission of experts, of committing war crimes in Yemen.

The situation has prompted a rare show of bipartisanship in the US Senate, as a coalition of politicians passed a resolution last year that would have ended the US's military support for the coalition.

Despite a Presidential veto of this legislation, and a certification by Secretary of State Mike Pompeo claiming the coalition had taken concrete steps to protect civilians, pressure has continued to mount for the US to withdraw its support for Saudi Arabia.

This political pressure is a step in the right direction. It is a recognition of the treaty-based obligations the US continues to breach through its myopic policy in Yemen.

Take the US's affirmative legal obligation under Common Article 1 of the four Geneva Conventions of 1949, which requires it to "undertake to respect and to ensure respect" for the Conventions in all circumstances.



The 2016 Commentaries on the Geneva Conventions, published by the International Committee of the Red Cross (ICRC), stipulate that Common Article 1 imposes a negative obligation on states not to encourage, aid or assist in violations of the Conventions as well as a positive obligation on states to do everything reasonably in their power to "prevent and bring such violations to an end". The ICRC posits that this duty is "particularly strong in the case of a partner in a joint operation".



The US has likely violated its negative obligation by continuing to furnish technical assistance to the coalition despite knowledge of credible allegations that the coalition has continuously violated international humanitarian law (IHL).



Reports of these IHL violations have continued even after Saudi promised the US that it would take steps to comply with IHL, which means that such violations have been foreseeable to the US for some time.



And the US could certainly be in violation of its positive obligation because the assurances it has received from Saudi (that it will take greater care to avoid indiscriminate targeting of civilians) are clearly not credible.

Thus, it is difficult for the US to argue that it is making reasonable efforts to prevent IHL violations when it accepts such empty assurances.

According to Larry Lewis, a former State Department Official who served as a senior civilian harm adviser under both the Obama and Trump administrations, US and Saudi officials have repeatedly stymied efforts to improve civilian protection programmes and promote accountability for civilian casualties.



For instance, during the Obama administration, Lewis attempted to help the coalition to create its own database to track the civilian casualties for which it was responsible, but he received little support from the government and he was eventually blocked from continuing his direct military-advisory function.

The civilian protection mechanism which does exist is also lacking in credibility: The Saudi-established Joint Incidents Assessment Team has been criticised by the UN for a lack of impartiality and transparency.

Lewis also notes that US officials have access to a database which pinpoints the role of American warplanes and munitions in any single coalition attack. But, despite concrete knowledge of the ways in which it aids and abets coalition war crimes, the US has refused to terminate its assistance. This behaviour hardly suggests an effort to "ensure respect" for the Conventions.

The US's legal failure over Yemen will have serious strategic consequences in the years to come.

First, the US has lost its moral credibility when it condemns war crimes committed in other armed conflicts. For instance, its denouncement of Russia's indiscriminate bombing of hospitals and schools in Syria rings hollow when it continues to arm and assist a coalition that is performing the same acts in Yemen.

Second, the US has arguably antagonised an entire generation of Yemeni civilians. Numerous civilians have found US-manufactured munitions at the scenes of some of the conflict's most egregious war crimes, such as the bombing of a school bus packed with children in August 2018.

Violent armed fighters are likely to feed off the resentment and heartache of those who have lost loved ones.

There is an important lesson the US can learn from these failures.

It is imperative that the US - and other European arms suppliers - develop a set of concrete standards for determining a "cutting off point" when lawful assistance - for example, technical support for allied nations engaged in armed conflicts - should cease.

The Office of Legal Counsel, a component of the US Department of Justice which provides legal assistance to the president and the Executive Branch agencies, has previously advised that the US government should re-evaluate the legality of its assistance when countries use US aid for unlawful purposes.

Such a re-evaluation would be a welcome step, but real change will require a more proactive solution. Future US presidents should engage Congress in developing a comprehensive framework for terminating US assistance in the face of continued violations of IHL.

European countries could readily follow suit. In fact, a recent decision by the UK's Court of Appeal demonstrates that EU countries would be wise to do so.

The court found that key UK ministers had illegally signed off on arms exports to Saudi Arabia without properly assessing the risk to civilians in Yemen.

This is a violation of Criterion 2(c) of the Consolidated EU and National Arms Export Licensing criteria, which requires the government to consider whether there is a "clear risk" that the equipment to be exported might be used in the commission of a serious violation of IHL.

Instead of letting the courts dictate the trajectory of its export licensing process, the UK and the US could proactively implement a framework which cuts off assistance to recipient countries which demonstrate no interest in IHL compliance.

President Trump's policy advisers have countered that cutting off support to the coalition at such a critical moment would cede control to the Iranian-backed Houthi rebels (who have also been credibly accused of war crimes) and that this would cost more Yemeni lives.

This argument misses the point entirely. Complete eradication of the Houthi rebels from Yemen would be nothing more than a Pyrrhic victory for the US.

This is because besting Iran in a proxy war means little when the US has abdicated its legal responsibilities, leaving a wake of civilian casualties and resentment.

Nations which are disdainful of IHL have undoubtedly taken note of the US's continued support for Saudi. They are likely to be emboldened to continue their own behaviour in other armed conflicts because they know the US's criticisms will be widely seen as hypocritical given its continued support for the Saudi coalition.

After five years of contributing to the world's worst humanitarian crisis, any geostrategic triumph will, therefore, be vastly outweighed by the damage the US has done to its legal and moral credibility.

It is time for the US to end its complicity in the atrocities in Yemen.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial stance.