Leaders from more than 50 nations ended a two-day summit in Washington on Friday with a pledge to make nuclear security an enduring international priority, while President Obama warned that roughly 2,000 tons of nuclear material around the world still require protection from terrorists.

The fourth Nuclear Security Summit produced plans to shift work once driven by periodic meetings of heads of government into permanent institutions, including the International Atomic Energy Agency, the United Nations and INTERPOL. The gathering also yielded new national commitments to remove or reduce stocks of highly enriched uranium, strengthen border detection and guard radioactive sources that could be used in a so-called dirty bomb.

Yet the meeting’s final communiqué made clear that the effort remains incomplete. It described nuclear and radiological terrorism as one of the greatest and continually evolving challenges to international security, reaffirmed that each state bears primary responsibility for materials and facilities under its control, and stopped short of establishing binding global standards.

Russia, which possesses one of the world’s largest inventories of weapons-usable material and participated in the first three summits, did not attend. Its absence underscored both the geopolitical strains surrounding the final summit and the limits of a voluntary process that has depended heavily on cooperation between Washington and Moscow.

Six years of removals and tighter security

Obama convened the first summit in 2010 after warning that nuclear terrorism represented the most immediate and extreme threat to global security. Since then, countries have removed or disposed of substantial quantities of highly enriched uranium and separated plutonium, improved physical protection at facilities and expanded efforts to detect trafficking across borders.

A White House accounting issued before this week’s meeting said all participating countries had reported progress in security practices. Thirty-seven had committed to greater cooperation against nuclear smuggling, 14 had promised better detection at ports and other transportation hubs, and 30 had established nuclear-security training and support centers.

At his closing news conference Friday, Obama said the United States had eliminated 138 tons of surplus highly enriched uranium—enough, by the administration’s calculation, for about 5,500 nuclear weapons. A separate U.S.-Russian program was on track to convert enough Russian uranium for about 20,000 weapons into reactor fuel used to generate electricity in the United States.

Argentina announced that it had eliminated its remaining highly enriched uranium, and Indonesia said it would remove all such material from civilian sites by September. Japan completed the removal of hundreds of kilograms of nuclear material from a research facility, including plutonium and highly enriched uranium supplied decades earlier by the United States.

The technical progress is significant because only a relatively small quantity of fissile material is needed for a crude nuclear device. But the danger is not confined to weapons-grade stocks. Radioactive sources used in medicine, research and industry are far more widely distributed and could be dispersed with conventional explosives, creating panic and costly contamination even without a nuclear detonation.

A permanent architecture after the summit

This week’s meeting was designed as the last in the current series, creating a problem the leaders tried to solve through five action plans. Instead of scheduling another summit, governments agreed to strengthen the institutions already responsible for nuclear security and to create a contact group that can preserve high-level coordination.

The plan gives the IAEA the most central role. Director General Yukiya Amano told an industry gathering that the agency helps countries manage cyber threats and secure the use, storage and transport of nuclear and radioactive materials, according to the agency’s March 30 account. The summit communiqué supported regular high-level IAEA conferences, beginning with a ministerial meeting planned for December.

A separate United Nations action plan calls for fuller implementation of Security Council resolutions requiring countries to keep weapons of mass destruction away from nonstate actors. Other plans seek stronger cooperation through INTERPOL, the Global Initiative to Combat Nuclear Terrorism and the international partnership that helps countries secure or eliminate dangerous materials.

The approach reflects a practical judgment: the work is too broad to be managed indefinitely by leaders’ meetings. Border agents must exchange information about traffickers; nuclear operators must test guards and accounting systems; regulators need the authority and independence to inspect facilities; and governments must prepare for theft, sabotage or cyber intrusion.

The summit also welcomed the approaching entry into force of the 2005 amendment to the Convention on the Physical Protection of Nuclear Material. Once enough countries ratify it, the amendment will expand legal obligations beyond international transport to include domestic facilities and material in peaceful use. It also requires cooperation to recover stolen material and respond to sabotage.

Russia’s absence and persistent gaps

The diplomatic framework is weaker without Russia. Moscow had worked with Washington for years to remove material from vulnerable sites, convert research reactors and dispose of weapons-grade uranium. But relations have deteriorated over Ukraine, Syria and other disputes, and Russian officials rejected the planning process for this summit.

Administration officials sought to separate that absence from the broader record. During a March 31 briefing, the White House argued that bilateral projects already under way would continue where possible. Obama nevertheless acknowledged that reduced cooperation makes further progress harder, particularly when both countries control such large inventories.

Analysts have also questioned the voluntary structure. A Brookings Institution preview noted that the summit process concentrated primarily on civilian material and did not create a comprehensive system of universal standards, independent assessments and public accountability. Most nuclear material remains outside civilian programs, and national reporting varies widely.

The final communiqué encouraged countries to invite peer reviews and share information without compromising sensitive security details. But it did not require inspections or establish penalties for weak protection. Progress therefore continues to depend on national decisions, technical assistance and political pressure.

Terrorist intent shapes the urgency

The Brussels attacks on March 22 lent added urgency to the discussions. Belgian investigators had previously discovered surveillance video involving a senior nuclear official during an inquiry connected to the Paris attacks, reinforcing fears that extremist networks may study nuclear facilities or personnel.

Obama said there was no indication that terrorist organizations possessed nuclear material, but he warned that groups such as the Islamic State had already used chemical weapons and would have no hesitation about pursuing far more destructive capabilities. The summit included a scenario exercise examining how governments would respond to a nuclear-security crisis, emphasizing the need for rapid communication and coordinated law enforcement.

British Prime Minister David Cameron’s office said the meeting brought together more than 50 states to strengthen controls and address nuclear and radiological terrorism. That breadth remains the summit process’s chief achievement and its central vulnerability: almost every government recognizes the danger, but protection is only as strong as the facilities, borders and institutions where failure is most likely.

The leaders leave Washington with fewer vulnerable stockpiles and a clearer division of institutional labor than they had six years ago. Whether that system can sustain political attention without another summit—and without Russia at the table—will determine whether the gains become durable barriers or a temporary high-water mark.