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David Cortright is a visiting scholar at Cornell University’s Reppy Institute for Peace and Conflict Studies and professor emeritus at Notre Dame’s Kroc Institute for International Peace Studies.

Read the companion piece here.

The 2015 Joint Comprehensive Plan of Action Iran Deal (JCPOA) was an historic agreement that established significant constraints on Iran’s nuclear program. The core bargain involved the acceptance of nuclear restrictions and transparency measures by Iran in return for the lifting of nonproliferation sanctions imposed by the US and UN Security Council. It was the result of several years of intensive negotiations with Iran led by the US, with the involvement of with the involvement of Britain, France, Germany, Russia, China and the European Union. Iran made significant concessions in accepting the agreement and complied fully with its terms. 

In 2013 Iran accepted and complied with an interim agreement, the Joint Plan of Action prefiguring the final accord, which required Tehran to restrict its uranium program and accept an enlarged International Atomic Energy Agency inspection regime. Iran complied with the interim agreement, building trust and laying the foundations for the final, more extensive joint comprehensive agreement.¹  

The JCPOA blocked Iran’s pathway to developing nuclear weapons and provided unprecedented monitoring and verification systems for assuring implementation. According to a 2017 public statement by dozens of former arms control officials and weapons inspectors, the JCPOA²

dramatically reduced the risk posed by Iran’s nuclear program and mandated unprecedented Iran Deal and transparency measures that make it very likely that any possible future effort by Iran to pursue nuclear weapons, even a clandestine program, would be detected promptly. By blocking Iran’s potential pathways to nuclear weapons, the JCPOA has also decreased the likelihood of destabilizing nuclear competition in the region. 

Details of the agreement

Under the terms of the JCPOA Iran dismantled more than 13,000 centrifuges and placed them in monitored storage. It shipped more than 11 tons of low-enriched uranium, 98% of its stockpile, out of the country. 

Iran also did the following:

1. Dismantled most of its centrifuges and reduced the number of operating centrifuges to 5,060 IR-1 machines for a ten-year period.
2. Agreed to cap the level of uranium enrichment for 15 years at 3.67 percent uranium-235, the threshold for medical use and far below the 90% level required for nuclear fission. 
3. For 15 years, confined enrichment to the Natanz site.
4. Ceased the production of additional IR-1 centrifuges for a decade
5. Maintained a lowered stockpile of uranium of all types equivalent to 300 kilograms.³

Iran’s potential pathway to a plutonium bomb was shut down. The core of its heavy-water reactor at Arak was removed and disabled. The facility was reconfigured with Russian and Chinese assistance so that it could not produce plutonium for nuclear weapons.⁴ Plutonium production fell ten-fold. Iran agreed to refrain from research or work on reprocessing spent fuel to extract plutonium for potential weapons for at least 15 years.

The JCPOA provided guarantees that Iran would not be able to have a nuclear weapon for at least a period of 15 years. To verify these terms, Iran accepted “accept the kind of inspections that no other country in the world has ever accepted”the kind of inspections that no other country in the world has had to experience, as Ali Vaez, the Iran project director at the International Crisis Group, stated.⁵

Verification

In signing the JCPOA Iran agreed to the most comprehensive and intrusive IAEA weapons inspection system ever negotiated.⁶ In all previous nuclear weapons inspections, the focus had been on fissile material, to verify that nuclear materials were being used only for peaceful purposes and could not be diverted to bomb production. The JCPOA went beyond this approach to look at potential bomb-making equipment. As Ali Vaez put it, inspectors examined “every nut and bolt” that could be used for centrifuges or other machinery involved in Iran’s nuclear production.

The Comprehensive Safeguards Agreement and the Additional Protocol established with the JCPOA created procedures granting IAEA full access to Iranian nuclear sites and other sites where undeclared activities were indicated. Under the terms of the agreement, scheduled to last 15 years, the IAEA had the right to access any site in Iran, including prompt entry to suspicious sites, in some cases within 24 hours.⁷ The agreement “undoubtedly placed Iran’s nuclear program under broader and stricter safeguards than existed before the accord,” wrote Olli Heinonen.⁸ The nuclear material monitoring mechanisms of the agreement were “robust.”

When Iran confirmed its acceptance of these terms, the UN Security Council unanimously adopted Resolution 2231 (July 2015) lifting sanctions.⁹  The resolution created the legal framework for member states to engage in economic trade, investment, banking, and travel with Iran. The termination of sanctions was the quid pro quo that motivated Iran to accept these strict limitations to its nuclear program.

Compliance

The record shows that Iran complied with the terms of the JCPOA.¹⁰ In testimony before the US Congress, officials from the Department of Defense, the State Department, and the US intelligence community stated that Iran was abiding by the agreement. In April 2018, the State Department’s official report on the agreement said Iran is “transparently, verifiably, and fully implementing the JCPOA” and reported no material breach of the agreement.¹¹ 

The IAEA issued more than a dozen reports on Iranian compliance from 2016 through 2018 and found no evidence of substantive Iranian violations of the agreement.¹² The reports described consistent Iranian fulfillment of its obligations under the agreement. Typical was the IAEA report of June 6, 2018,¹³ issued soon after the announcement of US withdrawal from the agreement. The report made clear that, contrary to claims by the Trump administration, Iranian officials were still implementing their obligations. Its findings included the following: 

1. Iran’s stockpile of low enriched uranium at that time was 123.9 kg, below the 300 kg limit set by the accord.
2. The number of installed IR-1 centrifuges at Natanz remained below the 5,060 limit set by the agreement.
3. Iran enriched uranium only to 3.67 percent uranium-235, the limit set by the deal. 
4. The stockpile of heavy water of 120.3 metric tons was below the negotiated 130 metric ton limit.

IAEA monitoring extended to all nuclear facilities, research and development activities, and all associated mining, milling and industrial production facilities. It is significant that the IAEA was able to measure stockpiles to the nearest 100 grams and enrichment levels to 3 figures. This was an indication of accuracy and added intelligence value of enhanced IAEA inspections and reporting.¹⁴ 

Official validation 

Many senior U.S. government officials and nuclear experts recognized the intelligence and security benefits of the JCPOA and urged the White House to continue to comply with the agreement. Former Republican Senator Daniel Coats, the Director of National Intelligence, stated in the directorate’s May 2017 Worldwide Threat Assessment that the JCPOA has “enhanced the transparency of Iran’s nuclear activities” and “extended the amount of time Iran would need to produce enough fissile material for a nuclear weapon from a few months to about a year.”¹⁵ Prior to commencing negotiations with Iran in 2013, that timeline would have been 2-3 months.

In October, 2017, Defense Secretary James Mattis confirmed that Iran was complying with the nuclear accord. When asked by then Rep. Ruben Gallego of the House Armed Services Committee if Iran was compliant, Mattis replied, “I believe fundamentally they are.”¹⁶ In September 2017, the Chairman of the Joint Chiefs of Staff, General Joseph Dunford, told the Senate Armed Services Committee that Iran was complying with the JCPOA and that withdrawal would have “unfortunate” ripple effects.¹⁷ Former Secretary of State Colin Powell described the JCPOA as “a pretty good deal” with a “very rigorous verification regime.”¹⁸ These and other security concerns were brushed aside in the decision to withdraw from the accord. 

Positive assessments of Iranian compliance also came from the governments of Britain, France, and Germany. Conservative British Foreign Secretary Boris Johnson said breaking the agreement would be a “mistake.” Former Israeli Prime Minister Ehud Barak said that Iran “kept the letter of the agreement quite systematically.”¹⁹ 

In October 2017, President Trump charged that Iran “has committed multiple violations” of the agreement and was preventing IAEA inspectors from doing their job. The website FactCheck.Org thoroughly debunked the claims. IAEA Director General Yukiya Amano issued a statement that “the IAEA has had access to all locations it needed to visit. … As I have reported to the Board of Governors, the nuclear-related commitments undertaken by Iran under the JCPOA are being implemented.”²⁰

Rejection

Evidence and informed opinion notwithstanding, on May 8, 2017 the White House officially reneged on the Iran deal and announced US withdrawal from the JCPOA.²¹ U.S. sanctions were reimposed and intensified. It was a day of infamy in the history of nuclear nonproliferation.

Iran continued to comply with the JCPOA into 2019, but in the face of continuing sanctions and hostility from Washington, Tehran abandoned its policies of nuclear restraint and began enriching uranium to higher levels. The country produced substantial amounts of higher enriched uranium, bringing their stockpile closer to levels that could be further enriched for the production of nuclear weapons. While IAEA inspectors remained in Iran, they issued alarming reports of Iran’s expanding enrichment program. A May 2025 BBC report cited an IAEA assessment that Iran possessed over 400kg of uranium enriched to 60% purity – far above the level used for civilian purposes. This was a nearly 50% increase in three months.²² 

These were dangerous developments that increased tensions in the region. They provided the justification Israel and the United States used to attack Iranian nuclear production sites during the 12-day war of June 2025.²³ Following the 12-day war, the Iranian government halted its cooperation with the IAEA and suspended verification visits at sites illegally bombed in June in violation of IAEA Safeguards agreements.²⁴ Tehran allowed IAEA inspectors back for  site visits at the civilian Tehran Research Reactor.²⁵ 

Although Trump said the June 2025 attacks obliterated Tehran’s nuclear capacities, the US joined Israel on February 28 2026 in renewed strikes against Iran’s nuclear capabilities, launching a devastating war that continues as of this writing. 

Read the companion piece here.

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