Executive Summary The expected conclusion of the joint U.S. –Israel military campaign against Iran will revive a long-standing debate: can military force effectively prevent nuclear proliferation, or does it merely delay it at high cost? For decades, a dominant view in policy and academic circles has held that diplomacy—through treaties, inspections, and economic incentives—offers a more sustainable solution than coercion. A close examination of the historical record challenges this assumption. Diplomatic frameworks such as the Nuclear Non-Proliferation Treaty (NPT) have established norms but have not prevented determined states from acquiring nuclear weapons. Negotiated agreements, including the 2015 Joint Comprehensive Plan of Action (JCPOA), have in several cases delayed nuclear progress without eliminating it. By contrast, the cases in which nuclear programs have been halted or reversed tend to fall into two categories: voluntary renunciation under specific geopolitical conditions, and disruption through military action or the credible threat thereof. The latter includes Iraq (1981), Syria (2007), Libya (2003), and most recently Iran (2026). The counterfactual case of North Korea—where military options were considered but not pursued—highlights the limitations of diplomacy in the absence of coercion. The historical record does not suggest that force is universally effective or cost-free. It does indicate, however, that diplomacy alone has rarely succeeded when states were determined to acquire nuclear weapons, and that coercive leverage—whether applied or credible—has often played a decisive role in shaping outcomes. Introduction: Iran and the Reopening of a Strategic Debate The joint U.S.–Israel military campaign against Iran in 2026 marks a decisive moment in the long-running effort to prevent nuclear proliferation in the Middle East. According to U.S. officials, the operation inflicted severe damage on Iran’s nuclear infrastructure, with President Donald Trump declaring that the program had been “obliterated.” Whether this assessment proves durable remains uncertain. What is certain, however, is that the end of the campaign will reopen a familiar debate: can military force prevent nuclear proliferation, or does it merely postpone it? For decades, much of the policy consensus in Western capitals has favored diplomacy over coercion. The underlying assumption has been that military action can at best delay nuclear progress, while negotiated agreements supported by verification mechanisms and economic incentives can provide more durable solutions. This logic was central to the design of the 2015 JCPOA, which sought to manage Iran’s nuclear ambitions through technical constraints rather than eliminate them through force. Yet this assumption has always rested on a partial reading of the historical record. A broader examination of nuclear proliferation over the past eight decades reveals a more complex pattern. Diplomatic arrangements have often failed to prevent nuclearization when states were determined to acquire nuclear weapons. Conversely, in several critical cases, military action—or the credible threat of it—has disrupted or terminated nuclear programs altogether. To assess the implications of the 2026 campaign against Iran, it is therefore necessary to revisit the historical experience of nuclear proliferation in its full empirical depth. I. Why Diplomacy Has Failed to Prevent Proliferation The effort to regulate nuclear weapons began almost immediately after their first use in 1945. The United States, aware of both the destructive potential of nuclear weapons and the risks associated with their spread, proposed placing nuclear energy under international control. The Baruch Plan envisioned a system in which the United Nations would oversee nuclear development and prevent its militarization. The Soviet Union initially refrained from rejecting the proposal outright but delayed engagement while pursuing its own nuclear program. Once Moscow successfully tested a nuclear weapon in 1949, it dismissed the plan. The opportunity for international control had passed. This early failure was not accidental. It reflected a structural feature of nuclear politics: states are reluctant to relinquish capabilities that they perceive as essential to their security. The Cold War entrenched this logic. The United States argued that it required a nuclear arsenal to compensate for Soviet conventional superiority in Europe, while the Soviet Union maintained that its conventional forces were necessary to offset America’s nuclear advantage. This circular reasoning prevented meaningful disarmament and ensured that nuclear weapons would remain central to great-power competition. Although arms control agreements later succeeded in capping and reducing nuclear arsenals, they did not prevent the spread of nuclear weapons. The United Kingdom (1952), France (1960), and China (1964) developed nuclear capabilities despite the absence of a formal international framework permitting such expansion. This initial group of nuclear powers—each a permanent member of the UN Security Council—was subsequently joined by additional states outside the treaty system: Israel in the late 1960s, India in 1974, Pakistan in 1998, and North Korea in 2006. The 1968 Nuclear Non-Proliferation Treaty sought to halt this process by institutionalizing a distinction between nuclear-weapon states and non-nuclear-weapon states. While the NPT has contributed to shaping global norms and has limited proliferation in some cases, it has not prevented determined states from acquiring nuclear weapons. India, Pakistan, and Israel never joined the treaty. North Korea joined in 1985 but withdrew in 2003 before developing nuclear weapons. Diplomatic efforts have repeatedly failed when confronted with strong strategic incentives. In 1976, Henry Kissinger attempted unsuccessfully to persuade Pakistan to abandon its nuclear program. Pakistan’s leadership, motivated by its rivalry with India and its perception of existential threat, chose to proceed. The combination of diplomatic pressure and economic considerations proved insufficient to alter this calculus. The same pattern has been evident in the case of Iran. Iran’s nuclear ambitions date back to the Shah, under whom the country pursued nuclear technology with Western support, including cooperation with Israel. Following the 1979 Islamic Revolution, the program was disrupted as many nuclear scientists fled the country. During the Iran-Iraq War (1980–1988), Tehran prioritized conventional warfare, but it resumed its nuclear efforts after the war, with assistance from the Pakistani scientist Abdul Qadeer Khan. In 2002, Iran’s clandestine nuclear activities were exposed by dissidents. The International Atomic Energy Agency declared Iran in breach of its NPT obligations in 2003, prompting negotiations with Britain, France, and Germany. Iran agreed in 2004 to suspend uranium enrichment, but the election of Mahmoud Ahmadinejad in 2005 led to the abandonment of this commitment. The United Nations Security Council subsequently passed resolutions demanding that Iran cease enrichment activities, but these measures failed to halt the program. This sequence illustrates a broader pattern: diplomacy can delay nuclear programs, but it rarely prevents them when states are determined to proceed. II. The JCPOA: A Case Study in the Limits of Negotiated Constraints The Joint Comprehensive Plan of Action (JCPOA) represented the most sophisticated attempt to constrain a nuclear program through diplomacy. The agreement imposed detailed technical limitations on Iran’s nuclear activities. Uranium enrichment was capped at 3.67 percent, well below weapons-grade levels of approximately 90 percent. Iran was limited to operating 5,060 first-generation centrifuges at Natanz for ten years, and its stockpile of enriched uranium was reduced to 300 kilograms for fifteen years. The Arak heavy-water reactor was redesigned to prevent plutonium production, and enrichment at the Fordow facility was halted and converted into a research center. The agreement also included an extensive verification regime, with the IAEA granted access to declared facilities and the ability to request inspections of undeclared sites. In exchange, Iran received significant economic relief, including the lifting of sanctions, access to frozen assets, and the resumption of oil exports and international banking. Despite these provisions, the JCPOA was structured as a temporary arrangement. Key restrictions were set to expire after ten to fifteen years, raising concerns that Iran would eventually be able to expand its nuclear program within the framework of the agreement. Critics argued that the JCPOA effectively legitimized Iran’s right to enrich uranium and enabled it to become a threshold nuclear state over time. The inspection regime also had limitations. Iran retained the ability to delay inspections of undeclared sites for up to twenty-four days, creating opportunities to conceal illicit activities. The agreement did not address Iran’s ballistic missile program, nor did it constrain its regional activities or support for proxy forces. Moreover, the economic benefits provided by sanctions relief strengthened Iran’s capacity to pursue its broader strategic objectives. Once international economic ties were restored, reimposing sanctions became more difficult, particularly as other countries resumed trade with Iran. The subsequent trajectory of Iran’s nuclear program confirmed these concerns. Following the U.S. withdrawal from the JCPOA in 2018, Iran resumed enrichment and gradually increased its capabilities. Its ability to withstand sanctions was facilitated by its economic relations with China. By the time of the 2026 military campaign, Iran had accumulated decades of nuclear knowledge and infrastructure, bringing it close to the threshold of nuclear weapons capability. The JCPOA thus illustrates the limits of diplomacy in altering the strategic calculus of a state that views nuclear capability as essential. III. When Do States Abandon Nuclear Programs? A small number of states have voluntarily abandoned nuclear ambitions, but these cases are often misunderstood. South Africa developed a nuclear arsenal during the Cold War, motivated by the need to deter Soviet-backed forces in neighboring states such as Angola and Mozambique. The program was supported by the country’s access to uranium and its relative isolation from Western security guarantees due to its apartheid regime. However, by the late 1980s, the strategic environment had changed. The withdrawal of Cuban forces from Angola reduced external threats, while economic sanctions and international isolation imposed significant costs. Seeking to improve its international standing, President Frederik de Klerk decided to dismantle South Africa’s nuclear arsenal. The country’s six nuclear weapons were dismantled in 1990, and it joined the NPT in 1991. Sweden’s case illustrates a different dynamic. During the early Cold War, Sweden explored the development of nuclear weapons despite its official neutrality. U.S. intelligence discovered that Sweden was close to acquiring tactical nuclear capabilities. To dissuade Stockholm, Washington offered enriched uranium suitable for civilian purposes but not for weapons. Accepting the offer would signal Sweden’s commitment to peaceful nuclear development, while rejecting it would reveal military intent. Under this pressure, Sweden abandoned its nuclear program in the mid-1960s. Other cases often cited as successes of diplomacy are less convincing. Argentina and Brazil ended their nuclear programs during transitions to democracy, but neither had reached advanced stages of weaponization. Ukraine, Kazakhstan, and Belarus relinquished nuclear weapons inherited from the Soviet Union under the 1994 Budapest Memorandum. However, these states did not abandon indigenous programs. Their decision to transfer nuclear weapons back to Russia has since been called into question, particularly in light of Russia’s invasions of Ukraine in 2014 and 2022, which undermined the security assurances associated with the agreement. These cases suggest that voluntary renunciation occurs primarily when the strategic rationale for nuclear weapons disappears or when external pressure reshapes incentives. Diplomacy alone has rarely been decisive. IV. The Decisive Role of Force and Coercion In contrast to the mixed record of diplomacy, several cases demonstrate the effectiveness of military action—or the credible threat of it—in halting nuclear programs. Iraq began pursuing nuclear technology in the 1970s and acquired a reactor from France in 1976. With the outbreak of the Iran-Iraq War in 1980, Saddam Hussein intensified efforts to develop nuclear weapons. In June 1981, Israel conducted an airstrike on the Osirak reactor, destroying the facility before it became operational. France did not rebuild the reactor, and Iraq’s nuclear ambitions were significantly delayed. Subsequent inspections following the 1991 Gulf War further constrained Iraq’s capabilities. Syria’s nuclear program followed a similar trajectory. In the early 2000s, Syria constructed a covert nuclear facility at al-Kibar with assistance from North Korea. The reactor was modeled on North Korea’s Yongbyon facility. In September 2007, Israel conducted an airstrike that destroyed the site. Syria subsequently bulldozed the remains in an effort to conceal the program. The operation effectively terminated Syria’s nuclear ambitions. Libya presents a case in which the credible threat of military action played a decisive role. In the 1990s, Libya pursued a clandestine nuclear program with assistance from Pakistani nuclear scientists Abdul Qadeer Khan. However, in 2003, following the U.S.-led invasion of Iraq, Libyan leader Muammar Gaddafi chose to abandon Libya’s weapons of mass destruction programs. The decision enabled the lifting of sanctions imposed after the Lockerbie bombing and reflected a reassessment of the risks associated with continued proliferation. Iran represents the most recent and strategically significant case. Despite decades of negotiations, sanctions, and partial agreements, Iran’s nuclear program continued to advance. The 2026 U.S.–Israel campaign sought to achieve what diplomacy had failed to accomplish: the destruction of key nuclear facilities and the disruption of Iran’s path to nuclear weapons. V. The Counterfactual: North Korea and the Cost of Restraint North Korea offers a revealing counterfactual. In 1994, the United States considered conducting airstrikes against the Yongbyon nuclear facility. Secretary of Defense William Perry and Assistant Secretary Ashton Carter developed detailed plans for targeted strikes and potential escalation scenarios, including the reinforcement of U.S. forces in South Korea. However, the operation was ultimately abandoned due to concerns about casualties, opposition from South Korea, and the possibility of a negotiated settlement. Former President Jimmy Carter’s visit to Pyongyang contributed to an agreement in which North Korea suspended its plutonium program. This suspension proved temporary. North Korea withdrew from the NPT in 2003, expelled IAEA inspectors, and conducted its first nuclear test in 2006. It has since developed a growing arsenal of nuclear weapons. The North Korean case highlights the limitations of diplomacy in the absence of credible coercion and underscores the importance of counterfactual analysis. The decision not to use force may have shaped the outcome as much as the decisions to use it in other cases. VI. The End of the Arms Control Era and the New Nuclear Order The global nuclear landscape is undergoing profound transformation. At the end of the Cold War, nuclear stockpiles declined significantly, from approximately 70,000 warheads in 1986 to around 12,500 in 2022. This reduction was the result of bilateral agreements between the United States and the Soviet Union, and later Russia. However, this trend has begun to reverse. Russia is modernizing and expanding its nuclear forces, while China is rapidly increasing its arsenal. Estimates suggest that China’s nuclear stockpile could reach 1,500 warheads by 2035. China is also developing a full nuclear triad, including land-based intercontinental ballistic missiles, submarine-launched missiles, and strategic bombers. The arms control framework is struggling to adapt. The New START treaty, which limits deployed strategic warheads, does not cover tactical nuclear weapons, where Russia maintains a significant advantage. Nor does it address emerging technologies such as nuclear-powered cruise missiles. The treaty is set to expire in 2026, and Russia has already announced the suspension of its participation. The nuclear environment is no longer bipolar. The United States now faces a three-way deterrence challenge involving Russia and China, each with distinct capabilities and strategic doctrines. Regional dynamics further complicate the picture, with India and Pakistan maintaining nuclear arsenals and North Korea continuing to expand its capabilities. In June 2024, Russia and North Korea signed a mutual defense treaty, adding another layer of complexity. Nuclear competition is also economic. The construction of civilian nuclear plants and the supply of enriched uranium have become instruments of geopolitical influence. Russia’s state-owned company Rosatom dominates global markets, exporting a majority of the world’s nuclear reactors and a significant share of enriched uranium. This creates dependencies even among Western countries and gives Russia leverage over energy policy. These developments suggest that the traditional tools of non-proliferation—treaties, inspections, and diplomatic engagement—may be increasingly inadequate in a more competitive and fragmented international system. Conclusion: Iran in Historical Perspective The historical record of nuclear proliferation does not support a simple conclusion. It does, however, challenge the assumption that diplomacy alone can prevent the spread of nuclear weapons. In multiple cases, negotiated agreements have delayed nuclear programs without eliminating them. By contrast, military action—and the credible threat of it—has in several instances disrupted or terminated nuclear ambitions. The effectiveness of such measures depends on specific circumstances, including timing, intelligence, and the broader strategic environment. They are not without risk, but their impact has often been more decisive than is commonly acknowledged. The 2026 U.S.–Israel campaign against Iran must be evaluated within this broader historical context. Whether it produces lasting results will depend not only on the destruction of infrastructure but also on Iran’s strategic choices and the international environment that follows. For policymakers, the key implication is not that force should replace diplomacy, but that the two are interdependent. Diplomacy is most effective when backed by credible coercive leverage, and least effective when such leverage is absent. As the global nuclear order becomes more complex and contested, reassessing the relationship between force and diplomacy will be essential for effective non-proliferation policy.