President Barack Obama has made his decision, and by the end of this year 10,000 U.S. soldiers will leave Afghanistan. By September 2012, 23,000 more shall do the same. And to ensure that Afghanistan remains secure, some tens of thousands of additional Afghan security forces will be trained by the U.S., with diplomatic efforts will follow. But whether or not the American withdrawal and the likely ensuing deal with the Taliban ends the conflict, it is certain that the consequences will have a major impact on Pakistan.

After the last American exit from Afghanistan following the Soviet war in that country, Arab jihadists took the Afghan mujahideen under their umbrella, and set up shop in Pakistan, an outcome that, given the current climate of instability and militancy, could easily happen again. As the Brookings Institution scholar Dr. Vanda Felbab-Brown said about the current conflict, "an unstable Afghanistan will be like an ulcer bleeding into an already extremely unstable, extremely hollowed out-Pakistan and will encourage only the worst tendencies in Pakistan. This will severely compromise our strategic objectives." History shows that the type of substance this ulcer bleeds exacerbates pre-existing problems in parts of the country, something that is especially true in the bustling port city of Karachi.

In the aftermath of the Soviet war, a massive quantity of weapons found their way to Karachi. Among the countless recipients were two criminal leaders already enmeshed in a turf war, Rahman "Dacoit" and Ghaffar Zikri. Both laid claims to territory in the Liyari neighborhood, and their trade included drugs and looting, respectively. The influx of guns made them far more dangerous not only to each other, but also to the communities over which they claimed kingship. In addition to using the weapons in their own street war, the two men were able to sell the valuable metal to other gangs who were not a threat to their space. The additional power they gained through the acquisition and sale of weapons served to expand their spheres of influence. Political parties leapt to patronize men such as Rahman and Zikri, using them as a means to exploit new area and gain authority, undermine their opposition, and, above all, secure votes.

Though these turf wars existed during the 1990s, but were limited to certain parts of the city. Today, however, the fight for space in the booming city has increased alarmingly. In the main this has to do with illicit planning activity, including land grabs by mafias often acting on the instruction of political parties, and fueled by mass migration into the city.

Since 2007, thousands of people have entered Karachi, particularly arriving from Khyber-Pukhtunkhwa province and Afghanistan. Pashtuns from both sides of the Durand Line have now become indiscernible to the common man. Indeed, despite the presence of Pashtuns who have been peacefully living in, and contributing to, the economic and social fabric of Karachi for decades, some of the many thousands coming in from the northwest represent a new breed bent on sending money to the tribal areas, some of which goes to fund terrorist activity. This has certainly blemished the common perception of the community as a whole, and contributed to a decrease in security in parts of the city. Some areas controlled by the Pashtun community have been unofficially declared "no-go" areas, where the police fight tooth and nail to gain entry. In one example, a Pakistani officer told me recently that surveillance of a small group of houses in Pashtun-dominated Sohrab Ghot culminated in the killing of four security personnel. Parts of Sohrab Ghot are now said to be run by tribal laws brought in by new migrants, and de-facto rogue leaders.

In this complex and dangerous environment where the state dares not tread, the procurement of weapons in Karachi has become a matter of survival. As tensions between different factions, be they ethnic, political, religious, or otherwise, increase, this survival moves into the critical stage of its evolution. As such, it is not uncommon today to visit Liyari or Sohrab Ghot and see guns displayed in houses.

Another factor impacting the security situation in Karachi is the influx of Taliban fighters, something that is not new but has increased over the years. Karachi, the economic center of Pakistan, provides both legal and illegal ways to gain access to large streams of revenue, which can be transported back to the tribal areas with ease. Pashtuns have for decades been the majority stakeholders of Karachi's transport industries, and the Pashtun community presides over areas which are close to the city's entry and exit zones, linking Karachi to the rest of Pakistan's industrial zones and the port. If a stranger approaches a truck-driver to deliver money on his journey to the northwest, the latter will likely not question the destination of the money or such a seemingly trivial request. Therefore, as Pashtun dominated areas grow and slip out of state control, and Taliban continue to flow into the city, the state's inability to police the Taliban via the Pashtun community will become more difficult, while the  Taliban will still be able to funnel money away from Karachi and into their operations.

An increased flow of arms following the departure of U.S. forces in Afghanistan will most certainly bolster the insularity and insecurity of such communities, leaving elements within them fully equipped to plan and execute terror. Though it is unlikely this terror will manifest itself directly in Karachi (one doesn't burn the land that feeds, and the city suffers from its share of violence as it is) it can certainly strengthen the Taliban presence elsewhere in the country. Unfortunately, the opportunities such a safe haven affords provide the ideal setting for enemies of the state to expand their presence, be they terrorists or local gangs. Their growth continues to spread slowly across a burgeoning Karachi, and Pakistan as a whole, with a potential to strengthen and supply the very actors that threaten people both inside, and out, of the country.

Bilal Baloch is a graduate student at the Fletcher School of Law and Diplomacy at Tufts University. He is currently conducting field research in Karachi.