Iran and North Korea are often rhetorically linked, most famously in President George W. Bush’s 2002 speech in which he labeled them part of an “axis of evil.” In practice, however, they have been largely treated as separate challenges for American foreign policy. There are good reasons for this. The Islamic Republic of Iran and the Democratic People’s Republic of Korea are in different regions, have different economies and political systems, and affect different sets of US allies.

Still, there are analysts and commentators who worry that the axis of evil is not simply a list of bad actors, but instead a team, whose members cooperate and assist each other. In public discourse, suspicions and accusations of Iran-North Korea cooperation are raised and then recede, only to return again when one or both countries are in the headlines. Recent allegations have run the gamut from speculation about new political ties between the two countries to claims that they are building a nuclear weapon together.

What are we to make of these allegations? Are Iran and North Korea in cahoots? As it turns out, while there are good reasons for suspecting cooperation between the two, the actual record is rather modest, limited to an earlier period of missile trade. There is no evidence of collaboration on nuclear weapons, despite numerous claims in the media. The prospect of future cooperation appears even more unlikely.

The logic of cooperation. At first glance, it would seem that Iran-North Korea military or even nuclear cooperation makes “sense.” Both nations face the United States as an adversary, and both have been subject to US and international sanctions. If my enemy’s enemy is my friend, then Iran and North Korea should be best friends forever. In addition, both Pyongyang and Tehran have demonstrated a willingness to cooperate in secret with foreign partners. Both countries received illicit assistance from the network founded by Pakistani nuclear physicist A. Q. Khan, and North Korea sold a nuclear reactor to Iran’s neighbor and ally Syria. Finally, both Iran and North Korea view missiles as a vital defense need (though for different reasons), and both have had clandestine nuclear weapons efforts.

While this logic seems to suggest that Iran and North Korea are meant for each other, the record of the last three decades points to a different conclusion.

Soon after the Iranian revolution ushered in the country’s current system of government in 1979, Tehran and Pyongyang did cooperate on missiles. During the Iran-Iraq War in the 1980s, Saddam Hussein rained missiles down on Iranian cities. North Korea provided Iran with ballistic missiles so that it could respond in kind. That cooperation continued into the 1990s but began to taper off by the end of the decade. As missile-defense expert Michael Elleman observed in 38 North,

…interviews with Russian and Ukrainian specialists aiding the Iranian missile program during the late-1990s suggest that cooperation between Pyongyang and Tehran was isolated and not comprehensive. Iran’s compartmentalisation of the missile programs would have impeded deep technical collaboration with North Korea, if not preventing it altogether.

The US intelligence community offered a somewhat different assessment, suggesting that missile cooperation continued into the 2000s. In 2006, Iranian officials acknowledged that they had received assistance from North Korea in the past, but said they had now established an indigenous program. By 2013, US Defense Department reports referred to Iran-North Korea missile collaboration in the past tense, and in early 2016, Director of National Intelligence James Clapper testified that “Of late… there has not been a great deal of interchange.”

On the nuclear front, there appears to have been no cooperation. Period. As the Congressional Research Service concluded in 2016, “no public evidence exists that Iran and North Korea have engaged in nuclear-related trade or cooperation with each other.” Indeed, neither the US intelligence community, nor the International Atomic Energy Agency, nor the UN Panel of Experts set up to support sanctions against North Korea has ever made such a claim. Likewise, virtually no journal article in the scholarly literature has suggested nuclear collaboration between Pyongyang and Tehran.

Unreliable sources. So where do these allegations come from? Unsubstantiated media reports. In preparation for Congressional testimony on Iran-North Korea collaboration, I reviewed some 76 media reports covering a span of 11 years, from 2005 to 2015. About a third of those were from media that most observers would associate with a particular ideological point of view, like the Free Beacon, the Tower, and Anti-War.com. Forty-two of these reports—more than half—were published in 2014 and 2015, as opponents of the Iran nuclear deal attempted to kill the agreement. In no case did these media reports provide any actual evidence for the allegations. It is worth noting in this context that the Directorate of National Intelligence concluded Iran had halted its nuclear weapons program in 2003, so claims of nuclear cooperation after that date would be especially questionable.

Why wasn’t there more of an Iran-North Korea partnership? One cannot know for sure why these two international outcasts did not cooperate more on missiles or at all in the nuclear domain. Someday, Iranian or North Korean officials might explain their reasoning, but in the meantime one can only speculate.

First, these are very different countries, in different geo-strategic positions, with very different national security objectives. As has become clear, North Korea’s main goal for its missile program is to develop an intercontinental ballistic missile (ICBM) capable of delivering a nuclear warhead to the United States. With that capability, the North would hope to deter a US attack and possibly drive a wedge between the United States and South Korea.

By contrast, Iran’s objectives were (and are) more limited and local, as Greg Thielmann recently pointed out on Lobe Log. It wanted to acquire a nuclear weapons capability, but as the US Director of National Intelligence repeatedly testified, had not made the political decision to build nuclear weapons. Iran also worried more about regional adversaries—Iraq, Israel, Saudi Arabia—and what it saw as a need to deter countries in the region with superior air power or missile capabilities. Put another way, it did not want to again find itself defenseless as it did during the Iran-Iraq War. Accordingly, Tehran has focused on shorter range, conventional ballistic missiles.

Second, the two countries occupy different positions in international politics. North Korea appears to relish its role as international bête noir, flaunting its nuclear aspirations and engaging in over-the-top rhetoric (only recently matched by another world leader). Iran, on the other hand, consistently denied that it was pursuing nuclear weapons. The denials were false, but they demonstrate the very different ways these two countries approached the same issue. This initial difference deepened in the wake of the Iran nuclear talks, a diplomatic process—beginning in 2013 and culminating with the Joint Comprehensive Plan of Action, or JCPOA, in 2015—meant to demonstrate that Iran was not pursuing nuclear weapons and to return the Islamic Republic to the community of nations. It would be odd for Iran to have signed up for all the restrictions and surveillance measures in the nuclear agreement if it intended to cheat with the North Koreans.

Finally there is an issue of risk, particularly for Iran. Iran and North Korea are the most-watched countries in the world. What were the odds that these two countries in different parts of the world could secretly collude without being caught? Could Iran tolerate the risk that a North Korean defector might spill the beans, or that the Pyongyang regime itself might collapse of its own weight, thus exposing an illicit relationship? In today’s international context, a Tehran-Pyongyang secret alliance would carry high risks with little benefit.

Motivated to mislead. Despite the ongoing absence of any evidence pointing to nuclear cooperation between Iran and North Korea, the claims continue. Why?

Perhaps one clue can be found in the sources and timing of the allegations. One might expect that accusations of Iran-North Korea collusion would show up in Asia, in particular from South Korean and Japanese sources. But that is not the case. Virtually all the claims originate in the United States and the Middle East. When the occasional claim does emanate from Asia, it invariably turns out to be an accusation by a US or Middle Eastern source that is being reprinted in the Asian press.

The timing of accusations is also notable, as they correlate quite strongly with the timing of domestic political fights in the United States over Iran policy. We see these allegations almost exclusively when the Iran nuclear deal is in the news and being attacked by its opponents.

In short, it would appear that these claims are more about politics than facts. If that assessment is correct, then we should expect outlandish and baseless accusations to continue, especially at moments when the Iran nuclear deal is most vulnerable, for example at the three-month intervals when the US president is required by law to certify to Congress that Iran is in compliance with the JCPOA. The next certification deadline is in April.

Of course someday, under different conditions, Iran and North Korea might collaborate on a nuclear weapons program. Prudence would therefore dictate that American policymakers keep watch for signs of such cooperation. Ironically, the most likely scenario for such collaboration would be if the JCPOA opponents get their wish, destroy the nuclear agreement, and pursue a policy of regime change against Iran. Then their dire warnings may finally be more than politically motivated mudslinging. They could then take “credit” for leading us down a path that produced the very outcome they had warned against.