“You are pitiful, isolated individuals! You are bankrupts. Your role is played out. Go where you belong from now on—into the dustbin of history!”

Thus in 1917 Leon Trotsky consigned the Mensheviks, the non-Bolshevik faction of the Russian Social Democratic Workers’ Party, to perennial insignificance—a fate from which they never recovered. Only five years ago, al Qaeda’s downfall appeared similarly imminent. Its founder and leader was dead. A succession of key lieutenants had been eliminated. And the region was transformed by the Arab Spring. Civil protest, it seemed, had achieved what terrorism had manifestly failed to deliver—and al Qaeda was the biggest loser. As John O. Brennan, then deputy national security advisor for Homeland Security and Counterterrorism and assistant to the president, told an audience gathered at a DC think tank in April 2012, “For the first time since this fight began, we can look ahead and envision a world in which the al Qaeda core is simply no longer relevant.” Less than a month later, on the first anniversary of al Qaeda leader Osama bin Laden’s killing, U.S. President Barack Obama proudly proclaimed that, “The goal that I set—to defeat al Qaeda and deny it a chance to rebuild—is now within our reach.”

How completely different it all looks today. In February, Director of National Intelligence James R. Clapper painted a singularly bleak picture of a newly resurgent al Qaeda alongside an ambitiously expansionist Islamic State (ISIS) in his annual worldwide threat assessment. Al Qaeda and its affiliates, Clapper told the Senate Armed Services Committee, “have proven resilient and are positioned to make gains in 2016…. They will continue to pose a threat to local, regional, and even possibly global interests….” More alarming still was the rise of an even more extreme offshoot. ISIS, he explained, “has become the preeminent terrorist threat because of its self-described caliphate in Syria and Iraq, its branches and emerging branches in other countries, and its increasing ability to direct and inspire attacks against a wide range of targets around the world.”

If a week is a long time in politics, five years is an eternity. It is easy to forget that, until very recently, there was no Islamic State ruled by ISIS; Abu al-Baghdadi’s putative caliphate was nothing more than a self-indulgent reverie. Indeed, the Sykes and Picot boundaries appeared indelible, and both Obama and Vice President Joe Biden were trumpeting the stabilization of democracy in Iraq and the attendant withdrawal of U.S. military forces as proof that “America’s war in Iraq” is “over.”

Given this concatenation of astonishing developments in so short a period of time, it very likely that more surprises will follow. In fact, by 2021 al Qaeda and ISIS might reunite—or at least have entered into some form of alliance or tactical cooperation. Although admittedly improbable in the near term, such a rapprochement would make a lot of sense for both groups and would no doubt result in a threat that, according to a particularly knowledgeable U.S. intelligence analyst whom I queried about such a possibility, “would be an absolute and unprecedented disaster for [the] USG and our allies.”

POOR PREDICTIONS

The United States suffers collective amnesia where terrorism and counterterrorism policy are concerned. After all, it was only recently that the conventional wisdom inside the Beltway was that the bloody split between al Qaeda and ISIS would consume, neuter, and ultimately destroy both groups. The conventional wisdom on al Qaeda has rarely been correct anyway, so it is not surprising that this particular expectation has proved to be little more than wishful thinking. And that is reason enough to explore why an al Qaeda–ISIS merger is not as farfetched as some wishfully contend.

A man purported to be the reclusive leader of the militant Islamic State Abu Bakr al-Baghdadi, July 5, 2014. Reuters There are at least four arguments that render this scenario plausible. First, the ideological similarities between ISIS and al Qaeda are more significant than the differences. Both groups fundamentally adhere to the principle first articulated by al Qaeda founding member Abdullah Azzam three decades ago: It is an obligation for Muslims everywhere to come to the defense of their brethren wherever they are threatened and endangered. In Azzam’s mind—as in bin Laden’s and current al Qaeda leader Ayman al-Zawahiri’s and ISIS leader Baghdadi’s—an aggressive, predatory war is being waged against Islam by its enemies. Those enemies are broadly conceived as infidels and nonbelievers, including the Western democratic liberal state, the corrupt and repressive Western-backed local apostates, and the Shia and other Muslim minorities. In this inevitable clash of civilizations, it is incumbent upon all Muslims to come to the defense of the worldwide Muslim community. The need for global jihad to defeat Islam’s supposed enemies is thus an integral aspect of both al Qaeda’s and ISIS’ ideology and mindset.

Both movements, moreover, share the view that the Western state system is inimical to the imposition of sharia (Islamic law). ISIS, for instance, regularly inveighs against democracy as that “wicked methodology.” In that regard, the group reflects al Qaeda’s own longstanding view of this system of governance. Like al Qaeda, ISIS also rails against the West’s control over Muslims’ most precious natural resources—oil and natural gas fields—and the established order’s creation and support of corrupt, compliant local apostate regimes that facilitate continued exploitation and expropriation.

Like al Qaeda in years past, ISIS similarly invites Western military intervention in Muslim lands, which, the group believes, will enervate the local regimes’ militaries and economies. “If you fight us,” ISIS proclaimed in 2014, “we become stronger and tougher. If you leave us alone, we grow and expand.”

Second, the differences that do exist between ISIS and al Qaeda are rooted more in clashing egos and tone than in substance. For now, the most salient impediment to reconciliation is the strong personal enmity and vicious rivalry between Baghdadi and Zawahiri. It is patently obvious that they loathe one another. Their dispute, however, seems to be predicated mostly on timing and process. In a nutshell, Zawahiri still argues that the far enemy has to be eliminated and Muslim lands completely cleansed of Western and other corrupt local influences before the caliphate can be established. Baghdadi, as the events of June 2014 showed, saw no reason to wait and instead took the offensive by attacking near enemies both in Syria and Iraq and declaring himself caliph.

The two men’s styles also differ. Baghdadi has created a cult of personality around himself that luxuriates in death and dismemberment; he’s more reminiscent of the Khmer Rouge’s Pol Pot or the Tamil Tigers’ Velupillai Prabhakaran than Azzam, bin Laden, or Zawahiri. Baghdadi’s megalomania is facilitated by his claims of a familial lineage that reaches back to the Prophet. His status makes a credible successor more difficult to identify. Accordingly, Baghdadi’s elimination could throw ISIS into total disarray and give al Qaeda an ideal opportunity to effect a voluntary or enforced reunification. For that matter, either Baghdadi’s or Zawahiri’s deaths could pave the way for a rapprochement, whether involving a consensual reunification or a hostile takeover of one group by the other. The attempted coup against Baghdadi in Raqqah in December 2014 by pro-al Qaeda ISIS members, however, suggests that a more likely scenario would be al Qaeda absorbing ISIS rather than the reverse. Regardless, the result would be a combined terrorist force of chilling dimensions.

A boy poses while showing one of the fake U.S. 100 dollar banknotes depicting Islamic State's leader Abu Bakr al-Baghdadi (L) and al-Nusra Front's leader Abu Mohammed al-Joulani (R), Syria December 27, 2015. Bassam Khabieh / Reuters The third argument in support of an al Qaeda-ISIS merger is that the two groups embrace the same strategy—albeit one more faithfully and viciously applied by ISIS. In fact, it is Baghdadi’s adherence to the al Qaeda playbook that arguably accounts for his rush in June 2014 to declare the resurrection of the caliphate and establishment of the Islamic State.

The strategy was set out by al Qaeda’s operational chief, Saif al Adl, in 2005. ISIS is currently at the fifth step in the seven-stage path. The first was the Awakening (2000-2003), which coincided with the 9/11 attacks, and is described as “Reawakening the nation by dealing a powerful blow to the head of the snake in the U.S.” That was followed by the Eye-Opening Stage (2003-2006), which unfolded after the U.S. invasion of Iraq and was allegedly designed to perpetually engage and drain the United States and the West in a series of prolonged overseas ventures. The Rising Up and Standing on the Feet Stage (2007-2010) involved al Qaeda’s proactive expansion to new venues of operations, as it did in West Africa and the Levant.

The fourth stage, the Recovery Stage (2010-2013), was originally intended to allow al Qaeda to consolidate its previous gains and catch its breath. In light of the death of bin Laden and new opportunities to topple apostate regimes afforded by the Arab Spring, this stage ended up having to be adjusted. Caught off balance itself by the uprisings sweeping across North Africa and the Middle East, al Qaeda scrambled to take advantage of the political chaos and vacuum of authority to reestablish its presence and exploit the internal upheavals as new opportunities for retrenchment and expansion. It was facilitated in this respect by the freeing of thousands of imprisoned jihadis and persons formally occupying key leadership positions. This fourth stage, in Adl’s strategy, would be followed by the Declaration of the Caliphate Stage (2013-2016) when al Qaeda would achieve its ultimate goal of establishing trans- or supra-national Islamic rule over large swaths of territory in the Muslim world. ISIS clearly stole a march on al Qaeda in this respect. The sixth stage, the Total Confrontation Stage (2016-2020), was meant to occur after the caliphate had been created and an Islamic army could commence the final “fight between the believers and the nonbelievers.” The final Definitive Victory State (2020-2022) comes when the caliphate ultimately triumphs over the rest of the world.

It is disturbing to see that, from ISIS’ vantage point, the movement is right on schedule. Likewise chilling is that the apocalyptic elements of the seventh and final stage are clearly evident in ISIS’ ideology and strategy. Its vision entails an eventual clash between Islam and the infidels prophesized to occur in Dabiq, Syria—which is the name chosen by the group for its online magazine. In other words, ISIS’ aims will never be exclusively local but, like al Qaeda’s, are global in ambition.

The fourth reason that al Qaeda and ISIS might eventually merge is that efforts to reunite the groups have been a regular feature of the behavior and rhetoric of both sides. ISIS portrays itself as the most faithful embodiment and effective agent of bin Laden’s vision and asserts that, under Zawahiri, al Qaeda has deviated from its historical mission and the grand ambitions it was once on the verge of achieving. In this respect, it is therefore not surprising that ISIS’ propaganda is profoundly reverential of bin Laden and deeply respectful of al Qaeda (although not al Zawahiri), referring to its soldiers, emirs, and sheikhs in a positive manner and continuing to glorify bin Laden’s accomplishments.

For his part, Zawahiri has been very careful in his publicly released statements to hold out the prospect of reconciliation. In a September 2015 statement, for example, he made this assertion:

I here confirm clearly and unequivocally that if there is fighting between the Crusaders, the Safavids, and the secularists, with any group from the Muslims and the mujahideen, including the group of Abu Bakr al-Baghdadi and those with him, then our only choice is to stand with the Muslim mujahideen, even if they are unjust to us and have slandered us and broke the covenants and stole from the Ummah and the mujahideen their right to consultation and selecting their Caliph, and evaded to be ruled by the Shariah in disputes.

These overtures are not exclusively rhetorical, as past serious attempts to achieve some modus vivendi make clear. On at least three occasions in the second half of 2014, the stars have almost aligned: in September, shortly after U.S. and coalition airstrikes against ISIS began in earnest; in November, after Baghdadi was incapacitated by a U.S. bombing run; and in December, following the coup in Raqqah.

PLAUSIBLE PROBLEMS

For almost a decade and a half, al Qaeda and the Salafist terrorist network that it spawned have defied Western efforts to bring the struggle to any kind of meaningful conclusion. Its longevity is as much a history of U.S. missteps and misreading of the threat as it is of adversaries’ enormous capacity for change, adaptation, and regeneration. The West now faces an enemy that has transcended terrorist tactics to evidence credible conventional military capabilities, which attests that the terrorist challenge has only become more variegated, diffuse, complex, and, quite simply, exponentially more difficult to defeat.

Osama bin Laden sits with his adviser Ayman al-Zawahiri, November 10, 2001. Hamid Mir / Reuters The insistent claims of the past five years that al Qaeda is poised on the brink of strategic defeat have been around longer than it took the United States to defeat Nazi Germany and Imperial Japan. It is difficult to imagine a worse constellation of terrorist threats than those posed by ISIS and al Qaeda along with their piebald affiliates and associates and franchises and provinces. Any kind of coordination of terrorist operations, much less a more formal modus vivendi, would have profound and far-reaching consequences for international security.

That scenario is no less plausible than the notion in 2014 that a Salafist movement would exercise sovereignty over parts of Iraq, Libya, and Syria, with multiple outposts in North, East, and West Africa, the Sinai, and Afghanistan. It is also plausible given the fact that this movement has withstood a concerted onslaught from the most technologically and doctrinally sophisticated military in history. That expectations of triumph have repeatedly been dashed by new tragedies such as the November 2015 Paris and March 2016 Brussels attacks is reason enough to take seriously the possibility of an ISIS–al Qaeda alliance.