A year ago, Pakistani officials at the highest level repeatedly told their American counterparts in the new Obama administration that there were no leaders of the Afghan Taliban in Pakistan. When asked what about the Quetta Shura—the top leadership of the Taliban that allegedly operated from Quetta in Pakistan’s Baluchistan province—they said it did not exist. When told the Shura was actually meeting at the same time as Obama’s team was reviewing Afghanistan and Pakistan policy, they denied the reports.

So when Pakistan detained Mullah Baradar, the No. 1 official in the Quetta Shura and the second in command of the Afghan Taliban this February in Karachi, Pakistan’s largest city, it was big news. Since then a half dozen or so other senior officials of the Taliban have been captured by the Pakistani intelligence service, the ISI. The Taliban’s eight-year-old safe haven in Pakistan no longer looks so safe—at least for some of its top commanders.

Naturally there is enormous speculation about why Pakistan is taking this action. For a year, the Obama team has been pressing Islamabad for just this sort of crackdown. The Bush team pushed for it when they were in power. Every senior American visitor to Islamabad has made a case for Pakistan to arrest the Taliban leadership. Clearly more than American encouragement—although that is useful—is behind the Pakistani policy shift.

It may be that the Pakistani army, which controls the ISI, came to the conclusion that the ties between the Pakistani Taliban—which it is now at war with—and the Afghan Taliban were too close and too dangerous. The two recruit from many of the same Pashtun tribes along the border and have long been allies. Pakistan last year very reluctantly went to war with its own Taliban jihadist Frankenstein, first in the Swat Valley and then in the tribal regions. The cost has been huge, with suicide bombings across the country. A Pakistani think tank estimates 25,000 Pakistanis were killed or wounded in the terror war last year—an unprecedented level of violence in the country’s 62-year history.

One senior Pakistani general told me late last year that he believed there was no difference between Afghan and Pakistani Taliban; they were all enemies of Pakistan. We don’t know if all the generals agree on that, but it is the simplest explanation. Other theories for the crackdown emphasize Pakistan’s desire to be a central player in any political process to end the Afghan War, a process President Hamid Karzai will discuss March 10 when he visits Islamabad. Arresting some of the Taliban may be a down payment for a seat at the table.

The truth is we just don’t know what is motivating the crackdown. Pakistan has seen the Afghan Taliban as an asset since 1994. The crackdown could, of course, be turned off just as quickly as it was turned on. It also does not appear to apply to other dangerous terrorist groups like Lashkar-e-Taiba, which attacked Mumbai from Karachi a year and half ago. The head of the group, Hafez Saeed, just publicly threatened that Pakistan must wage jihad against India at a large rally, and India has raised its terror alert level this week.

While we seek to better understand what is going on in Pakistan, we should also be prepared to take yes for an answer. If the top leadership of the Taliban no longer enjoys a sanctuary across the Durand Line, the border drawn by England between Afghanistan and Pakistan a century ago, then the prospects for Obama’s war in Afghanistan improve. As long as the enemy of the NATO forces in Afghanistan could operate with relative immunity in Pakistan, NATO’s mission was going to be very difficult. If the Pakistanis now police their side of the Durand Line differently, NATO will find the job easier, although still bloody and expensive.

It is also worth noting that many of the arrests are taking place in Karachi. The Daily Beast reported weeks ago that the head of the Taliban, Mullah Omar, had probably switched his hideout to Karachi from Quetta. This huge port city has a long history of being a hangout for terrorists. Khalid Sheikh Mohammed watched the Twin Towers collapse from an Internet café in Karachi on September 11, 2001, and he trained the Saudi musclemen for the job in the city. It is the epicenter now of the global struggle against al Qaeda and its allies like Lashkar-e-Taiba and the Taliban.