The Taliban was toppled in Afghanistan in 2001 for harboring al-Qaeda, but it has not been defeated. With an estimated core of up to sixty thousand fighters, the Taliban remains the most vigorous insurgent group in Afghanistan and holds sway over civilians near its strongholds in the country’s south and east. It has also metastasized in neighboring Pakistan, where thousands of fighters in the country’s western tribal areas wage war against the government. Now, as the international combat mission in Afghanistan closes, the Taliban threatens to destabilize the region, harbor terrorist groups with global ambitions, and set back human rights and economic development in the areas where it prevails.

Though the Taliban appears unlikely to dismantle the Afghan government and revive its emirate, it poses the most serious challenge to Kabul’s authority even as the United States winds down the longest war in its history and NATO scales back its largest-ever deployment outside of Europe. The insurgents’ resilience calls into question a state-building project that has cost its international backers hundreds of billions of dollars.

The U.S.-led military coalition has suffered nearly 3,500 dead and more than ten thousand wounded. Since 2001, at least twenty-one thousand Afghan civilians have been killed in conflict, and three million people have been displaced, according to the UN refugee agency. Afghan troops and police are dying at their highest rates ever.

The drawdown of international forces from Afghanistan also raises questions about Pakistan’s strategy in South Asia and its leverage over the Afghan Taliban. The insurgents could not have thrived without sanctuary in Pakistan, whose main intelligence service, the Inter-Services Intelligence (ISI) directorate, cultivated them in the 1990s and maintained ties to them after 2001 (PDF). Pakistan has long sought what its military doctrines call strategic depth: an amicable regime in Kabul, to avoid being encircled by its chief rival, India, to the east, and a pro-India Afghanistan to the west.

Along with several foreign militant groups, Pakistani Taliban factions thrived in the sanctuaries along the frontier that the Pakistani military had set aside for the Afghan Taliban. But Pakistan does not control the Islamist militancy it helped enable, and its military is now fighting a movement whose primary aim differs from that of the Afghan Taliban. The Pakistani Taliban has declared Islamabad apostate for aligning itself with post-9/11 U.S. foreign policy and seeks revolution in Pakistan. Under the umbrella Tehrik-i-Taliban Pakistan (TTP, or Taliban Movement of Pakistan), these militants have attacked Pakistani security forces and civilians nationwide.

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