Countless world leaders have gathered in the Netherlands for the third Nuclear Security Summit. U.S. president Barack Obama convened the first summit back in 2010 in an effort to rein in the supposed growing threat posed by the spread of nuclear weapons and materials. If the level of participation in these summits is any indication, this perception is broadly shared across the international community.

It is also wrong. By nearly any objective measurement, the world is winning the war against nuclear weapons. Nuclear weapons have spread far more slowly than anyone predicted, and today the threat of nuclear proliferation is at an all-time low. Moreover, the trend lines are all positive.

There are at least five reasons for nuclear optimism.

1) The Great Nuclear (Dis)Arms Race

During the Cold War, the U.S. and Soviet Union engaged in a rapid and utterly pointless nuclear arms race. In 1950, the superpowers maintained just 304 nuclear weapons between them; by the time of the Cuban Missile Crisis in 1962, they possessed nearly 29,000 of them, a 9,439 percent increase. By 1986, the size of the superpowers’ combined arsenals had more than doubled to 68,000 warheads.

Although this history is well known, the nearly as rapid de-nuclear arms race is usually noted only to reference its supposed shortcomings. But the U.S. and Russia have reduced their nuclear arsenals nearly as quickly as they built them up. By 2013, Moscow and Washington had less than 4,000 deployed nuclear weapons, a 94 percent decrease from 1986. By 2018, this number will further drop to just 3,000 nuclear weapons under the terms of the New START Treaty. This is less than 74 percent of what was allowed under the first START Treaty, and President Obama has called for further cuts.

Although the superpowers denuclearization is most pronounced, they are by no means alone. Great Britain has more than halved the size of its nuclear arsenal since 1981, and France has cut its nuclear stockpile by 44 percent since 1992. Moreover, since 1989, four nuclear-armed powers—South Africa, Ukraine, Kazakhstan and Belarus—have voluntarily disarmed completely. At most two nations—Pakistan and North Korea—have acquired them during this time.

And while some of the other nuclear-weapon states are increasing the size of their arsenals, they are doing so by tens of warheads. The days when states maintained thousands of nuclear weapons are nearing their end.

2) Nuclear Apathy

If actual nuclear arsenals are declining, the greater nuclear proliferation threat must come from countries and groups that have yet to acquire them. Indeed, the U.S. has elevated the threat posed by the spread of nuclear weapons in recent years. The 2010 Nuclear Posture Review, which outlines U.S. nuclear policies, stated that “changes in the nuclear threat environment have altered the hierarchy of our nuclear concerns and strategic objectives. In coming years, we must give top priority to discouraging additional countries from acquiring nuclear weapons capabilities and stopping terrorist groups from acquiring the materials to build nuclear bombs.”

In fact, the threat posed by the spread of nuclear weapons is drastically declining, and it is now possible to talk about a “great proliferation slowdown.” Two causes undergird this slowdown.

The first is the growing number of states who are uninterested in acquiring nuclear weapons. This is well documented by Harald Muller and Andreas Schmidt’s comprehensive study of nuclear-weapons programs between 1945 and 2005, which found that “states with nuclear weapons activities were always a minority, and today they are the smallest minority since 1945.” Specifically, in 2005 they identified ten states as having nuclear-weapons activities (including those with nuclear weapons), less than six percent of UN members. Notably, the states with the greatest ability to acquire nuclear weapons—such as Germany, Brazil, Japan and South Africa—are also among the least interested in them.

3) Nuclear Failures

While interest in nuclear weapons dwindles, the few outliers to this trend have been increasing unsuccessful in their attempts to build the bomb. In fact, the historical record is directly at odds with the common assertion that globalization and the diffusion of nuclear knowledge has made it easier to build nuclear weapons. As Jacques Hymans has noted, before 1970, seven nations began serious nuclear programs and all seven succeeded in an average of seven years. Since 1970, however, only three of the ten nations that initiated serious nuclear-weapons programs have been successful, with the jury still out on Iran. Moreover, the three nations that succeeded in building a nuclear arsenal took an average of 17 years to do so. The Islamic Republic of Iran, for its part, reconstituted the Shah’s nuclear program no less than thirty years ago.

4) The Success of the Nuclear Non-Proliferation Treaty

The fact that the spread of nuclear weapons has declined also calls into question the frequently made claim that the Nuclear Non-Proliferation Treaty (NPT) is at serious risk of unraveling.

Indeed, in both its popularity and effectiveness, the NPT is one of the most successful treaties ever negotiated. This is evident, first and foremost, by the widespread adherence it enjoys. A total of 190 countries are party to the treaty, far more than any other arms-control agreement in history. Despite an explicit clause giving parties the right to withdraw from the treaty, a grand total of one country has ever elected to do so—North Korea. Suffice to say, the Hermit Kingdom is not an international trendsetter. In fact, in 1995 the parties to the treaty unanimously decided to extend it indefinitely. Many states in recent years have also voluntarily granted the International Atomic Energy Agency expanded enforcement authority by signing onto the Additional Safeguard Protocol.

The NPT has also been remarkably successful in practice as well. Not a single signatory has ever been able to acquire nuclear weapons on its watch. That’s not from a lack of trying. A number of countries have tried to fool IAEA inspectors over the years—including Iraq under Saddam Hussein and North Korea. Each time, they have been surprised by the sophistication of the IAEA’s detection and safeguard measures.

5) Nuclear Terrorism

Still, many contend that the greatest proliferation danger today comes from outside the state system. As President Obama has put it, “the single biggest threat to U.S. security, both short term, medium term and long term, would be the possibility of a terrorist organization obtaining a nuclear weapon.”

If accurate, this merely says that the U.S. is remarkably safe. While the prospect of Al Qaeda acquiring an atomic bomb is terrifying, the truth is that the group has never shown significant interest in going nuclear. Even at its apex before 9/11, Al Qaeda expressed only a passing interest in atomic weapons, which was dwarfed by the time and resources it put into non-nuclear attacks. For example, an Al Qaeda defector claimed in early 2001 that AQ earmarked $1.5 million to purchase uranium in 1994. Although this figure was later disproven, it is nowhere near the amount of money that would be required to manufacture a nuclear weapon. By way of comparison, Israel estimates that Iran’s nuclear program has cost at least $160 billion, about 106,566 percent more than Al Qaeda had earmarked.

Whatever interest Al Qaeda may have had in nuclear weapons before 9/11, it has almost certainly lost it in the period since. Before the 2001 attacks, Al Qaeda had prided itself on carrying out large, sophisticated and expensive attacks against the United States. Since that time period, the group has evolved toward preferring cheaper, less sophisticated attacks like the postal mail bombing attempt in 2010. Since it has failed to even succeed in these fairly simple attacks, it’s unthinkable that it would even attempt the astronomically more difficult task of nuclear terrorism.

If it decided to try, however, it would certainly fail. There is no chance that Al Qaeda could build and maintain an enrichment or reprocessing facility undetected anywhere in the world. Thus, it would need to buy or steal the requisite fissile material. However, thanks to a number of initiatives since 9/11—such as the Proliferation Security Initiative (PSI) and the Nuclear Security Summits—procuring these materials would be far more difficult today than before the 2001 attacks. Since Al Qaeda didn’t come close to obtaining a nuclear bomb in the much more passive pre-9/11 environment, it’s unthinkable that it could succeed in the much more hostile post-9/11 world. That’s probably why it hasn’t tried.

Zachary Keck is Associate Editor of The Diplomat where he authorsthe Pacific Realist blog. He can be found on Twitter @ZacharyKeck.