The Taliban’s smooth and rapid transition after their acknowledgment of Mullah Mohammad Omar’s death sends a strong message: They are afraid of the potential rise of Daesh (the self-proclaimed Islamic State of Iraq and the Levant) in Afghanistan if they fail to project unity. That reality should be useful to the US government as it tries to negotiate a transition deal with the Afghan government and the Taliban. It’s still true that the Taliban can demand something close to de facto control as part of the deal. But now, the Taliban have an incentive to talk that didn’t exist before the rise of Daesh. They have something to lose if the country devolves into congeries of competing warlord-controlled territories.

The man who will replace Omar, Mullah Akhtar Mohammad Mansour, was Omar’s deputy and has been effectively leading the Taliban since Omar’s death, and perhaps before that. His selection seems to suggest that the Haqqani Network, a faction that has gradually become powerful enough to rival the Quetta Shura within the Taliban, was willing to compromise on leadership, rather than pressing for Omar’s son, whom the Haqqanis were rumoured to favour.

The two deputies to Mansour, however, are one of the leaders of the Haqqani Network and a former Taliban judge who is said to be close to the Haqqanis. That signals a kind of grand compromise between the Quetta Shura and the Haqqanis, who’ve struggled for dominance over the years.

The most logical conclusion is that both the Quetta Shura and the Haqqanis have concluded that, at this moment, projecting Taliban unity is much more important than their squabbling. Further underscoring this interpretation is that the announcement seems to have been made in haste, to follow immediately on the public acknowledgment of Omar’s death. Not all the Taliban leaders were present when the decision was made, another indicator of time pressure.

What explains the unity and dispatch among the famously factious and patient Taliban? The answer is almost certainly the recognition that lapses in Taliban authority could have major consequences now. What’s changed for the Taliban is the rise of Daesh.

To be sure, the Daesh players in its Syrian-Iraqi heartland are both geographically far from Afghanistan and politically disconnected from Pashtun alliances at the heart of the Taliban’s complex structure. But Daesh has presented itself as the symbolic alternative for any organisational entrepreneur who might want to form a new, competing, alternative to the Taliban.

In Libya, also far away from Daesh territory, similar organisational entrepreneurs have taken advantage of the power vacuum and labelled themselves as belonging to the group. The name alone carries a programme of eventual unification, and a now-familiar strategy of expanding to take over territory within ungoverned space. (It hasn’t been said enough that Daesh follows a version of the “build and hold” or “inkblot” strategy advocated by the US military’s counterinsurgency manual.)

In Afghanistan, a Daesh alternative is the only plausible option to displace the Taliban. There can be no doubt that some Afghans would share the objectives of the Sunni militant group.

And Daesh aspires, as a definitional and existential matter, to rule the entire Islamic world. The Taliban calls itself an “emirate,” and Mansour is its new emir, or prince. Daesh claims a caliphate — and under classical Islamic constitutional thought, an emir owes formal allegiance to a legitimate caliph. In the construct of Daesh ideology, it trumps the Taliban.

The potential Daesh threat to the Taliban is a boon to the US - a small glimmer of a silver lining in the gathering cloud of the Daesh threat. Until now, the structural problem with peace talks between President Ashraf Gani’s government and the Taliban has been that the Taliban have little incentive to give up the fight. The Afghan government can’t ultimately control much territory without US support — and that support has appeared to be of limited duration. The right tactical move for the Taliban has therefore been to keep fighting at a moderate level and wait patiently for the US to pull back and Gani’s government to collapse.

Now the Taliban can see a potential cost associated with the slow collapse of the government and the country. Gradualism begets disorder, a power vacuum and internal Taliban strife. In other words, the longer it takes for the Gani government to fall, the greater the chances for Daesh to undermine the Taliban. The Taliban want to avoid a situation in which, having won their long war against the US and its Afghan puppet regime, they have to fight another civil war against an Daesh offshoot.

The Taliban therefore should favour a deal with the Afghan government that lets them consolidate de facto power before Daesh can make further inroads. Because the true US goal is now to see transition in Afghanistan without mass revenge killings and the immediate, absolute suppression of women throughout the country, it should seize the moment.

Admittedly, this result of a more rapid transition to the Taliban is so modest that it might seem horrific. But this is Afghan politics, which means it’s a game of worst-case scenarios. And in the end, more civil war in Afghanistan followed by the possibility of Daesh moving in is worse for the US than a de facto Taliban regime. And the Taliban know it.

—Washington Post

Noah Feldman, a Bloomberg View columnist, is a professor of constitutional and international law at Harvard and the author of six books, most recently Cool War: The Future of Global Competition.