Since at least January, ISIL has been operating a franchise along the Afghan-Pakistan border, which it calls the “Khorasan province,” so-named for the ancient land that now encompasses both countries. Led initially by a former Pakistani Taliban commander, the group is said to be composed mainly of disaffected fighters from the Pakistani and Afghan Taliban. Many of them had lost faith in the reclusive Mullah Omar — who, Afghan officials said this week, has been dead since 2013 — and pledged their allegiance to ISIL’s self-declared caliph, Abu Bakr al-Baghdadi.

Now analysts suspect the death of Mullah Omar, confirmed by the Taliban on Thursday, will open the door for mass defections from the Taliban and perhaps even Al-Qaeda, since the religiously binding bayat — declarations of loyalty — that flow downward from the late Taliban leader to sub-commanders within these networks will be in question.

Mullah Omar’s death will “send shockwaves through the major jihadi schools in the Muslim world, especially Al-Qaeda and the Taliban,” said Hassan Hassan, the author of a recent book on ISIL’s rise and a fellow at the Chatham House think tank. Both groups have been under “enormous pressure” since Baghdadi’s audacious announcement of a caliphate across Syria and Iraq — a longtime pipe dream for Al-Qaeda that directly challenged its pre-eminence atop the movement — and his group's astonishing military success, accomplishments that have drawn thousands of recruits from across the globe. “The challenge for ISIS was not that many of the rank-and-file of those organizations did not sympathize with it but that they felt tied to their groups by a binding pledge of allegiance,” Hassan said, using another acronym for ISIL. “Since Mullah Omar is now dead, this is a golden opportunity for ISIS to recruit among the Al-Qaeda and Taliban sympathetic base."

The crisis is perhaps most acute for Al-Qaeda, ISIL’s chief rival and forebear, which has been relegated to the sidelines since the two split in 2013 over tactical and leadership disputes. As recently as last year, Al-Qaeda’s leader, Ayman al-Zawahiri, had reaffirmed his allegiance to Mullah Omar — who for years sheltered Osama bin Laden, Al-Qaeda's founder — in a video that also announced the establishment of a Qaeda franchise on the Indian subcontinent. If the Afghan government is correct that Omar had died in a hospital in the Pakistani city of Karachi more than a year earlier, Zawahiri made that pledge to a dead man. That would suggest “that Zawahiri was either ignorant or duplicitous, neither of which will endear him to his followers,” said intelligence consultancy The Soufan Group, in a recent analysis.

Hassan said all eyes will be on Africa, Southeast Asia and Central Asia, where ISIL has thus far struggled to gain a foothold due to traditional Al-Qaeda support in those regions. But there could be shifts among even Al-Qaeda's strongest franchises, too: Both the Nusra Front, in Syria, and Al-Qaeda in the Arabian Peninsula, based in Yemen, might decide they have been released of their bayat to Mullah Omar (by way of Zawahiri’s now-spurious pledge) and abandon a movement they have surpassed in some respects.

ISIL is already making its move in Afghanistan. In his latest address, Baghdadi made a point of specifically welcoming followers of the Hanafi school of Sunni Islam — to which the Taliban belongs — into the caliphate. On the ground, Khorasan has already won a handful of skirmishes with their Taliban rivals and taken over several villages in the eastern Nangarhar province. Top Khorasan commanders — including, reportedly, its so-called governor, Hafiz Saeed Khan — have even been targeted by recent U.S. airstrikes, revealing Washington's anxieties about ISIL finding fertile ground in yet another country that U.S. forces have only recently left behind.

Separate from the ISIL challenge, Taliban watchers predict a period of internal fracturing over key questions such as Mullah Omar's successor (Mansour) or whether to pursue peace talks with the hated, U.S.-backed government in Kabul. At this week's Taliban meeting where Mullah Akhtar Mohammad Mansour was named the new leader, Reuters reported that the son and brother of Mullah Omar as well as other senior figures walked out in protest.

There was already believed to be virulent dissent against the decision of certain Taliban leaders to sit down with Afghan President Ashraf Ghani’s administration for peace talks, the latest round of which were slated for Friday. Experts theorized that anti-peace elements within the group kept these divisions under wraps only because Mullah Omar was said to be supportive of the peace process. On July 15, a message supposedly drafted by Mullah Omar himself was posted to the Taliban’s website, declaring that talks and armed struggle could occur simultaneously.

As it turns out, that message came from the grave, spurring questions about if and why top Taliban commanders had been kept in the dark about their leader's demise. Such ambiguities have been endemic to the group since Mullah Omar went underground, and could play right into ISIL's hands. “Many Taliban have been unhappy about their leader being quiet for so many years, but they have no reason to stick it out anymore,” said Michael Kugelman, a South Asia expert at the Wilson Center in Washington, D.C. Baghdadi has “tried to supplant Mullah Omar by casting himself as the real ‘Commander of the Faithful,' so he’ll be a logical shift for many disaffected militants.”