In my Foreign Policy column, I discuss the odds of the Afghan conflict mutating again, this time into an old-fashioned war between Afghanistan and Pakistan.

Rather than winding down with the planned departure of NATO troops by 2014, the war in Afghanistan may just be undergoing a metamorphosis, as has happened many times since strife began there in the late 1960s. A slowly escalating old-fashioned war between Afghanistan and Pakistan may soon emerge, joining the internal insurgencies both of those governments are attempting to smother and pitting one state against the other. Cross-border sanctuaries and Islamabad's covert support to the Taliban are well-known features of the current violence. But as the Western military presence inside Afghanistan draws down, the trends leading to direct military escalation between Afghanistan and Pakistan are likely to continue.

The Afghan government will face an increasingly difficult security situation after 2014 and will need a new strategy if it is to survive. The number one security problem from Kabul's perspective is the continued presence of Taliban sanctuaries inside Pakistan, and the support the Afghan Taliban continues to receive from Pakistan's intelligence service. For a decade, U.S. and Afghan officials have pleaded with the Pakistani government to halt this support, to no avail. For Islamabad, groups like the Haqqani Network -- which specializes in periodic raids in downtown Kabul -- are proxy forces that Pakistan can use to keep Afghanistan weak and pliant.

After 2014, the Afghan army and police will bear nearly the full burden fending off the Haqqanis and other cross-border Taliban forces. Afghan military leaders are likely to conclude that they cannot reach a stable end-state by only parrying the Taliban's attacks. The only hope of ending the war on favorable terms is through offensive action against the Taliban's sanctuaries in Pakistan or action that inflicts pain on the leadership in Islamabad. If Kabul hopes to negotiate a settlement with Islamabad and the Taliban, it will have to acquire some leverage first. And that will come only after it has demonstrated a capacity to threaten the Taliban's sanctuaries and other assets inside Pakistan.

Initial trials of such incursions may have begun. Last week, the Pakistani government accused the Afghan National Army of a cross-border raid into the Upper Kurram District. Two Pakistani tribesmen were killed during a 90-minute gun battle. Although this particular incident may be more a case of hot pursuit rather than a deliberate attack, it also shows the Afghan army's willingness to step up its aggressiveness.

The Afghan government may also find it useful to employ the same tactics that Islamabad is using against Afghanistan. Pakistan has its own problem with Taliban insurgents, with these rebels using the Afghan side of the border as a sanctuary from Pakistani security forces. Indeed, in June, a Pakistani Taliban raiding party crossed from its Afghan sanctuary into Pakistan, captured 18 Pakistani soldiers, and videotaped the severed heads of 17 of these prisoners. Pakistan's army chief Gen. Ashfaq Pervez Kayani subsequently complained to U.S. Marine Gen. John Allen, the coalition commander, and urged him to take action to control the Taliban sanctuaries inside Afghanistan.

It seems doubtful that the Pakistani Taliban finding haven in Afghanistan are agents of Afghanistan's intelligence service. But the Afghan government has likely concluded that it needs to obtain leverage over Pakistan if it is to obtain a satisfactory settlement to the war. If the Pakistani Taliban lurking in Afghanistan are a potential source of that leverage, it might be only a matter of time before Kabul makes contact with the Pakistani rebels.

Kayani probably realizes that there is as little chance of him getting a positive response from Allen and Karzai as there is of Pakistan doing anything meaningful about the Taliban problem that runs from east to west. That would explain why the Pakistani Army is taking matters into its own hands the old-fashioned way. Beginning in March, it fired a series of cross-border rocket barrages targeted at suspected Pakistani Taliban base camps in Afghanistan's Kunar province, resulting in the deaths of four civilians.

The Haqqani attacks in Kabul and against U.S. targets in eastern Afghanistan have compelled U.S. officials to consider cross-border special operations raids against Haqqani camps inside Pakistan. Given the military hardware currently in place, the intelligence on the Haqqanis the United States has developed, and the experience its special operations raiders have accumulated, U.S. forces are unlikely to ever get a better opportunity to hit the Haqqani Network and thereby create some incentives for a settlement. But the White House currently has a higher priority, namely disengaging from the conflict. Secretary of State Hillary Clinton's apology to Pakistan for a cross-border "friendly fire" incident last November that killed 24 Pakistani soldiers has reopened the supply lines from Afghanistan to the port at Karachi, which the United States will need to extract its mountain of equipment by the end of 2014. The requirements of an orderly withdrawal trumped the risks of widening the war and further angering Islamabad.

Although the United States can withdraw from Afghanistan, the Afghans, at least the vast majority of them, cannot. They are stuck with the Haqqanis, Pakistan's intelligence service, and Islamabad's long-term interest in a weak Afghanistan. The only path to a reasonable settlement lies through offensive action inside Pakistan. Afghans will have to be willing to go where the U.S. military (drones excepted) have feared to tread.

Until the Afghan military can develop greater offensive punch, it will have to turn to proxy forces such as the Pakistani Taliban as tools to gain leverage over Islamabad. Should such proxies fail, Kabul will have to turn to an outside power to support its development of helicopter mobility and artillery and air support, essential elements of a capability to directly attack the sanctuaries and other objectives inside Pakistan.

When he signed the strategic partnership agreement pledging support to Afghanistan through 2024, it is unlikely that President Barack Obama had such a war in mind. But once Kabul becomes solely responsible for Afghanistan's security, it will undoubtedly turn to the United States first to help it develop the offensive capability it believes it will need. Should Washington demur, Kabul will call New Delhi, which could be eager to help.

After 2014, Pakistan should see the wisdom in wrapping up the remainder of al Qaeda and settling the conflict with Afghanistan. NATO's withdrawal will actually reduce Islamabad's leverage and expose it to more forms of pressure. Continuing the conflict will only encourage outside intervention.

If Islamabad decides to fight on after 2014, we should expect to see a messy, multi-level conflict much like the 18th century French and Indian War. That war featured insurgencies, proxy armies, old-fashioned nation-state war, and great power intervention from the far side of the world. A similarly complicated scenario may be headed for the Durand Line. The Afghan war may be about to mutate again -- policymakers should get ready for the change.