The past year’s national security news has been dominated once again by terrorism.  Terrorist attacks in Paris, Mogadishu, Istanbul and Brussels — to name just a  few — have been carried out by increasingly violent groups like Al-Shabaab, Boko Haram and the Islamic State. While those attacks have been horrific, security experts fear the fallout we’d see if any of those groups were to carry out a major attack using nuclear, biological, or chemical weapons.

It is possible. We already know that ambitious, violent groups and individuals – like the Islamic State and al-Qaeda and its offshoots – are trying to find the materials they need for an attack using weapons of mass destruction (WMDs).

Preventing them from doing so is challenging. It’s not just a matter of strong domestic controls over those technologies. Groups could acquire the materials necessary for an attack using WMDs in one country and launch attacks in another. The Islamic State reportedly has already done this, using chemical weapons in an attack on a town near Kirkuk in northern Iraq.

Nor can any single government seal its borders securely against such an attack. Preventing a WMD attack will require global cooperation. And while efforts to prevent nuclear proliferation and terrorism through processes like the Nuclear Security Summit are high profile, the United Nations has worked below the radar for some time on an arguably more ambitious effort to prevent the full range of WMD terrorism.

The world’s only universal non-proliferation agreement 

These efforts started in 2004, when the U.N. Security Council passed Resolution 1540, which obligated all nations for the first time to adopt policies and practices that would keep the financing, technologies and materials needed to create WMDs out of the hands of “non-State actors.” There were already agreements in place that aimed to control the spread of WMDs among states, of course. UNSCR 1540 sought to address threats posed by terrorist groups, a.k.a. non-state actors.

In effect, the resolution obligates the world’s nations to police their own corporations, commerce and citizens, preventing them from financing, selling or giving the elements of such weapons to non-state actors and mandating “appropriate effective” trade controls on international commerce. Because it was passed under the Security Council’s Chapter VII powers, Resolution 1540 became a binding international legal obligation for all U.N. member states.

This also makes UNSCR 1540 the world’s only universal non-proliferation agreement.

UNSCR 1540 was controversial when it passed. On one hand, it came after the 9/11 terrorist attacks and public revelations that the Pakistani nuclear weapons scientist AQ Khan had used a network of private companies to evade non-proliferation controls and sell nuclear technologies to Pakistan. On the other hand, the U.S. had invaded Iraq the year before on the pretext that Saddam Hussein had been developing WMDs. So while growing concerns about WMD terrorism lent the effort a lot of political will, the U.S. invasion of Iraq also bolstered fears that the Security Council would seek to punish non-compliance in some serious way. UNSCR 1540 also meant the U.N. was touching on vital issues of national security. Still others objected because the obligations set by 1540 would be costly and difficult.  In general, UNSCR 1540 represented a substantial expansion of the Security Council’s Ch. VII authority, and states not involved in the decision-making pushed back.

Since that rocky start, however, the vast majority of the world’s states have come around to supporting and engaging it. That’s in part because supporters have not pushed for enforcing 1540 through threats or sanctions, but have relied on sharing expertise and providing support in meeting the standards for countries that need it, as we’ll explain below.  As a result, UNSCR 1540 is changing how states confront a major threat to global security.

UNSCR 1540 has these three unique assets in keeping terrorists from getting WMDs

There’s obviously no way to quash all violent extremists. Groups like al-Qaeda and the Islamic State are resilient. New groups can form almost anywhere in the world. Fortunately, most such extremists have no interest in WMD terrorism. Those that do (such as Aum Shinrikiyo in the 1990s or al-Qaeda and Islamic State today) have had little success when they’ve tried.

The challenge is to make sure it remains difficult to get the materials, technologies, and knowledge needed to build, deliver and use those weapons, even as they become more economical and more available on global markets.

That’s what UNSCR 1540 aims to do, in three main ways.

1. UNSCR 1540 is comprehensive, bringing many different weapons under one rule.

Before UNSCR 1540, arms control efforts were piecemeal and uneven, with different agreements restricting specific categories of weapons. The UNSCR 1540 approach subjects all WMDs to the same standard. Additionally, its “bow to stern” approach covers not just the weapons themselves but also the financing, manufacturing, production and transport of any WMD element.

2. UNSCR 1540 is a global mandate, binding everywhere, unlike previous nonproliferation treaties and conventions.

UNSCR 1540 is a global standard, requiring all to adopt policies to prevent WMD proliferation. That’s not true for any other non-proliferation instrument, including the Nuclear Nonproliferation Treaty (NPT) and the biological or chemical weapons conventions. Many countries — North Korea, India, Pakistan and Israel, to name a few — have avoided signing or ratifying some of those agreements. They are required to comply with UNSCR 1540, which gives UNSCR 1540 substantial potential to influence global non-proliferation efforts.

3. UNSCR 1540 encourages compliance rather than imposing punishments.

The Security Council’s Chapter VII powers allow the body to impose a full range of measures, such as sanctions, to enforce 1540’s obligations. But instead of relying on imposing costs for non-compliance, the Security Council formed the 1540 Committee and a Group of Experts to help coordinate and promote global compliance efforts.

The Committee includes Security Council member representatives and is responsible for monitoring implementation, matching assistance providers with requests for assistance, and reporting on overall progress. The Group of Experts reaches out to governments, educates them about their nonproliferation responsibilities and advises them on effective policies and measures.

Tellingly, the U.N. Security Council over the years has passed continuing resolutions that broaden the 1540 Committee’s mandate and emphasize such creative engagement – over coercive enforcement.  Experts with whom we’ve spoken say they use the obligation created by UNSCR 1540 to encourage states to act.

So is it making a difference?

Yes, although its final effectiveness at preventing WMD proliferation is impossible to judge at this point. While UNSCR 1540 isn’t fully implemented, supporters have been remarkably successful at getting states to accept the resolution’s obligations as legitimate.

For example, governments no longer question the validity of the resolution, although they disagree about how broad the mandate is and how quickly they must meet the obligations. And while less than a third of the U.N.’s member states bothered to submit the required initial reports in the first year, today more than 90 percent of the world’s governments have met their reporting requirements and worked with the Committee on implementation.

Of course, reporting is not the same as actually preventing the spread of dangerous materials – but without the initial report, little else can be done. Many states are reporting more than they have to. Early opponents like South Africa and Malaysia are now leaders in lagging regions, encouraging other governments to do their part and funding outreach. Global non-proliferation experts now talk about 1540 as central to global security efforts.

What’s more, UNSCR 1540 seems to be affecting policy and practice. Four avenues stand out. First, to implement the mandate, many governments are using standards, rules, and procedures gleaned from other nonproliferation efforts, like that of the Nuclear Suppliers Group and Missile Technology Control Regime. This increases the number of states working to meet the high standards for non-proliferation that those important agreements set.

Second, the nuclear deal negotiated with Iran last summer uses UNSCR 1540’s “bow to stern” wording as the standard for Iran’s re-entry into the global economy. This is a strong indication that the 1540 approach is becoming a common non-proliferation framework.

Third, because UNSCR 1540 groups all WMDs together, experts can learn from the experience of other fields. They have come to realize, for example, that biological hazards aren’t as well-monitored or controlled as are nuclear and chemical weapons, and are working to catch up.

Finally, governments since UNSCR 1540 have been passing more comprehensive laws to regulate trade in WMD-related technologies. In passing those new laws — laws designed to make it harder for violent non-state actors to acquire the materials, technologies, and knowledge needed to create WMDs — they often cite their UNSCR 1540 obligations.

In other words, UNSCR 1540 has raised the standards for how governments become “good non-proliferation citizens,” and governments are working to meet those standards.

The work has just gotten started

The work has really just started. It will be years before the mandate is fully implemented worldwide. And it’s hard to evaluate success; we’ll never know what WMD attacks (if any) might have happened without the resolution’s efforts.

Nevertheless, the 1540 Committee, the global non-proliferation community, civil society, and academics are working to assess effectiveness. Currently, the 1540 Committee is conducting a comprehensive review of the resolution’s performance, to understand its strengths and weaknesses. That has included civil society fora soliciting feedback and suggestions from nonproliferation experts and concerned groups.

The committee will host another forum — with nations, international organizations, and civil society — at the United Nations June 20-22, 2016.

UNSCR 1540 in some ways rewrites the non-proliferation rule book. Our political leaders, technical experts, academics and civil society have a stake in remaining engaged in the debate over its future.

Bryan R. Early is an associate professor of political science and director of the Project on International Security, Commerce, and Economic Statecraft (PISCES) and the Center for Policy Research at the University at Albany, SUNY.

Mark T. Nance is an assistant professor of political science in North Carolina State University’s School of Public & International Affairs and co-director of the Energy & Security Initiative.