ISIS-K is Forcing the Taliban to Choose Between Iran and Jihad
There's a sense of history coming full circle in the ISIS-K suicide bombing of a Shiite mosque in Afghanistan.
ISIS, the original one, started out as Al Qaeda in Iraq. But it broke from Osama bin Laden and the Al Qaeda leadership in Afghanistan\Pakistan by unrelentingly targeting Shiites in Iraq over and above even the United States.
While Al Qaeda pleaded with ISIS to focus on killing infidels, ISIS accurately bet that exploiting Sunni-Shiite tensions would win it far more popularity in Iraq than killing Americans. After the U.S. withdrawal and Iran's growing power in Iraq, ISIS rode the backlash to build its own brand, going from Al Qaeda in Iraq to ISIS, and playing a key role in the Sunni-Shiite civil wars in Iraq and Syria.
ISIS then began making inroads into Afghanistan by recruiting among the Haqqani Network, which is the part of the Taliban that's closest to Al Qaeda. ISIS-K's leader came out of the Haqqani Network.
The Taliban is an umbrella group and ISIS is using tried-and-true methods to make the Taliban and Al Qaeda seem like weak appeasers in order to break off units, commanders, and fighters.
The suicide bombing of a Shiite mosque in Afghanistan which allegedly killed and wounded some 100 Shiites is the ISIS-K strategy for forcing the Taliban and Al Qaeda to choose between Iran and the Jihad.
The Taliban don't care much for Shiites and there has been fighting with Shiites in the past, but right now they're trying to maintain good relations with all the major players. Their hold on Afghanistan is unstable and they want to maintain good relations with Iran.
Iranian's Shiite Islamists have bad memories of the Taliban from the 90s and there are resentments going back a long way. With NATO out of Afghanistan, Iran will be under more pressure to protect Shiite minorities in Afghanistan.
(It helps to understand much of the Muslim world not in terms of borders and national flags, which are artificial concepts injected by the West, but by intersecting geographies of tribe, ethnicity, and religion which often overlap and spill over past national borders based on past invasions and migrations going back for a long time, and which led to feuds that still simmer today.)
To simplify... ISIS-K is going to make the Taliban look bad by going after Shiites so that it can accuse them of not being true Muslims. (This is the ISIS house style.) The fight is a classic power struggle, but Jihadists would look bad if they admitted that what they're really fighting over is who gets the drug money, the satellite dish and the 4 wives, and so a pretext is required to trigger the conflict.
Afghanistan's Shiite situation isn't as toxic as it is in Iraq or Syria, but the tensions are real, and by making this conflict a referendum on killing Shiites, ISIS-K is positioning itself as the true Jihad while making the Taliban look like they're the protectors of the Shiites.
Will it work? Probably to some degree. Despite the Taliban's claims that they have the country secured, expect ongoing fighting to continue indefinitely. A lot of people claimed to have control of Afghanistan, but the rural areas are all but impossible to secure, and the tribal culture and the incentive for fighters to go on fighting is such that a forever war is all but inevitable. All it takes is some money and a reason.