Internal Struggles

In some ways, additional U.S. forces in the country could further undermine the ANSF. The Taliban use the presence of foreign troops on Afghan soil to advance the narrative that their country is under occupation and to recruit new fighters to their cause. The group has also made the withdrawal of foreign forces a precondition for participating in peace talks. Despite the dangers of staying in the country, however, NATO forces understand that withdrawing troops from Afghanistan would be riskier still. The Taliban would likely take more territory — perhaps eventually claiming enough land to effectively reconquer the country. Though the United States is open to a power-sharing agreement that includes the Taliban in the interest of ending the war, it won't tolerate a government led by the group. After all, the last Taliban administration abetted transnational extremist organizations such as al Qaeda by hosting them on Afghan territory.

Afghanistan's mountainous terrain, meanwhile, defies unified governance and economic development alike, posing additional challenges to the peacemaking effort. The dearth of tax revenues makes it even harder for the central government in Kabul to project power in the country's hinterlands or, for that matter, to adequately fund its military. The country's complex milieu of ethnic groups, meanwhile, adds to the difficulties of governing. The current National Unity Government, for example, rests on a shaky compromise between President Ashraf Ghani, a member of Afghanistan's largest ethnic group, the Pashtun, and Chief Executive Abdullah Abdullah, an ethnic Tajik. The Taliban have skillfully exploited Kabul's limited reach by installing shadow governors in provinces across the country and establishing courts to mete out justice in accordance with Islamic law. Until the central government has addressed its shortcomings, the Taliban will continue to win hearts and minds in Afghanistan as they wage their insurgency.

Friends in High Places

The Taliban, moreover, has a powerful ally on their side — and just across the border. Pakistan has admitted to hosting elements of the Taliban's leadership on its territory and even nurtured the organization during its infancy, helping the group sweep across southern Afghanistan on its way to conquer Kabul in September 1996. Islamabad's long-standing support for the Taliban reflects its own national security interests: Installing a government in Afghanistan that shares some of its priorities would enable Pakistan to guard against potential encirclement by its archrival, India.

Islamabad's strategy derives in part from its experience with the Bengali independence movement of 1971. India intervened in the conflict that ensued to help East Pakistan achieve its independence as Bangladesh. In the process, Pakistan lost a chunk of its territory and half its population. Islamabad is determined to keep the episode from repeating in its restive western territories along the Afghan border, including Balochistan in southwest Pakistan. The province is home to a secessionist movement whose exiled leaders have sought India's assistance in their campaign against Pakistan's government. Cultivating a relationship with the Taliban offers Islamabad a way to keep neighboring Afghanistan from falling into India's orbit by ensuring that it will have a say in the country's post-war future.

Crossing the Line

The Durand Line, the 2,430-kilometer (1,510-mile) border that separates Pakistan and Afghanistan, has historically facilitated this effort. The border, which cuts through the inhospitable terrain of the Hindu Kush mountains, is porous, enabling Islamabad to project influence into Afghanistan through its support for the Taliban. But after 15 years of war on the other side, the boundary's permeability has become more of a liability than a selling point for Pakistan. Militant inflows into the country have aggravated Pakistan's own internal security problems, prompting Islamabad to try to secure the border. As Islamabad clears the way for a merger between its Federally Administered Tribal Areas and neighboring Khyber-Pakhtunkhwa province, it is even putting up fencing along the Durand Line so that it can devote greater military attention to India.

But effective border management will require Afghanistan's cooperation — something that Pakistan is unlikely to secure. For one thing, the ANSF is already stretched thin in its nationwide fight against the Taliban. For another, by guarding the border, Afghanistan would be recognizing the Durand Line's legitimacy, which it has long contested. Enforcement along the boundary will remain lax, giving militants the continued leeway to launch attacks from the border regions into both countries — and further complicating efforts to end the war.

Beyond the number of soldiers deployed in Afghanistan, a complex set of factors underpins the conflict there. Even if a troop increase alters the stalemate in the Afghan government's favor, the ANSF and the Taliban will keep hammering away at each other until one of them relents. As the Taliban reportedly once put it, the United States has "the watches and we have the time." Trump will have to consider these factors as he decides whether to recommit his country to its longest-running war.