Above: Seized weapons believed to have been sent by Iran for delivery to Houthi forces in Yemen. Image via US Navy.

Yesterday, the Treasury Department levied sanctions against five Iranian officials for smuggling ballistic missiles to Yemen, which violated a UN Security Council Resolution. This is only the first of what will likely be many steps toward ensuring that Iranian missiles no longer reach Yemen. But it is an important one.

Many observers will likely see the sanctions as part of the Trump administration’s desire to isolate and punish Iran after withdrawing from the JCPOA earlier this month. That may be true. But it is also true that the war in Yemen will continue as long as Iran is smuggling missiles into the country, providing a crucial weapon for the Houthi forces fighting the Saudi-led coalition. Cutting off this supply of missiles is vital to isolating the Houthis and forcing them to negotiate.

For the past two years, along with four colleagues, I have been monitoring the targeted sanctions program in Yemen for the UN Security Council. During that time we produced four reports on the war – two public and two private – along with several case studies, totaling well over 1,000 pages. But our conclusions can be broken down into three simple points: all sides have violated international humanitarian law, sanctions are not working, and there is no military solution to the conflict.

A diplomatic solution is possible but only if the two main parties to the conflict – the Saudi Arabian-led coalition and the Houthis – agree to negotiate in good faith. So far, that has not happened.

Instead, there have been feints at peace while war continues, devastating Yemen’s civilian population. The UN Secretary General has called Yemen “the world’s worst humanitarian crises,” and it is easy to see why. Cholera has returned to Yemen, as has diphtheria, potable water is disappearing, infrastructure is nearly non-existent, and medicine along with the skilled doctors to administer it is increasingly hard to find.

Al-Qaeda and ISIS carry out near-daily attacks, the internationally recognized president is in exile, the south is attempting to secede, and proxy militias on all sides have turned much of the country into a Mad Max world where laws no longer apply. Suspects are disappeared, detainees are tortured and left to bake in unventilated shipping containers, schools and hospitals are bombed from the air, while on the ground houses are dynamited and political assassinations have become commonplace.

What we call the war in Yemen is actually three separate yet overlapping wars: a civil war, a regional war, and a war against terrorism. But it is the regional war that is key. This is the war that features an Arab coalition led by Saudi Arabia and the UAE and backed by US fuel, weapons, and intelligence against a group known as the Houthis, who receive support – including smuggled ballistic missiles – from Iran.

This is the war that began in March 2015, when Saudi Arabia initiated airstrikes in an effort to reinstall Yemen’s president, Abdo Rabbu Mansour Hadi, whom the Houthis had overthrown in a coup. A war that was supposed to last weeks is now in its fourth year with no end in sight.

Militarily, the Saudi coalition has three basic options left. It can withdraw completely, leaving the Houthis in control, essentially legitimizing the coup. The coalition could insert a massive influx of ground troops into Yemen for what would be a long and bloody ground war with no guarantee of success. Or it can do what it has been doing for the past four years – conduct airstrikes – and hope for a different result.

None of these options are attractive or likely to do much to bring an end to a war that is costing Saudi Arabia billions of dollars a month and wrecking Yemen for generations to come.

What the lack of viable military options does mean, however, is that Saudi Arabia and its coalition partners will sit down, negotiate, and compromise. The Houthis, however, will not. And it is this central imbalance that is prolonging the war.

The Houthis will travel for talks, they will sit at a table, and they will listen. They want the recognition and the trappings associated with being treated like a government. But they will not make any counter-offers and they will not enter into negotiations. The simple reason is that they don’t think they have to.

The Houthis believe they are in a stronger position and that they can wait the Saudis out. After all, they control the capital of Sanaa, most of what passes for government institutions in the north, and a sizeable portion of Yemen’s highland territory. They are also under little pressure. With few exceptions, the Houthis’ top leadership has been largely insulated from both airstrikes and the shortages associated with this war. Indeed, many of their militia commanders are actually making money by controlling a lucrative black market trade.

Similarly, UN sanctions, designed to pressure Houthi decision makers, have failed. The targeted sanctions program in Yemen relies on an asset freeze and a travel ban. But the three Houthis who have been sanctioned by the UN Security Council don’t have international bank accounts and don’t travel abroad. Sanctions, at least in Yemen, are meaningless.

What does matter to the Houthis is Iranian support, particularly smuggled Iranian ballistic missiles. In January the Panel of Experts on Yemen, on which I served, found Iran in non-compliance with a UN Security Council resolution that prohibited the supply of weapons to the Houthis.

The Security Council, however, failed to take any action or hold Iran accountable for this violation. Instead, after a Russian veto, the council could only agree on a technical rollover. The wording of the resolution, the framework for negotiations, everything remained the same as the year before, as if Iran had not been guilty of non-compliance.

The Security Council’s failure to enforce its own resolution not only encourages future Iranian weapons smuggling but also reinforces the Houthis’ assumption that they don’t have to negotiate.

Only when the international community ensures that Iranian missiles no longer reach Yemen will the Houthis be forced to both sit at the table and actively engage in peace talks. Until that happens the war will continue, and the world’s worst humanitarian crisis will get even worse.