Five years ago this month, an American-backed Kurdish and Arab militia ousted Islamic State fighters from a village in eastern Syria, the group’s last sliver of territory.

Since then, the organization that once staked out a self-proclaimed caliphate across Iraq and Syria has metastasized into a more traditional terrorist group — a clandestine network of cells from West Africa to Southeast Asia engaged in guerrilla attacks, bombings and targeted assassinations.

None of the group’s affiliates have been as relentless as the Islamic State in Khorasan, which is active in Afghanistan, Pakistan and Iran and has set its sights on attacking Europe and beyond. U.S. officials say the group carried out the attack near Moscow on Friday, killing scores of people and wounding many others.

In January, Islamic State Khorasan, or ISIS-K, carried out twin bombings in Iran that killed scores and wounded hundreds of others at a memorial service for Iran’s former top general, Qassim Suleimani, who was targeted in a U.S. drone strike four years earlier.

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