Pakistani paramilitary troops patrol a tense area of Karachi in April 2009, after armed ethnic clashes between Pashtun and Urdu-speaking groups left at least 34 people dead in Pakistan's financial capital, Karachi. Asif Hassan/AFP/Getty Images hide caption

itoggle caption Asif Hassan/AFP/Getty Images

A Pakistani truck driver shows the damage to a NATO truck after being attacked by militants in Karachi, Pakistan. In 2009, there were about 40 attacks on NATO supply trucks coming from Pakistan. Fareed Khan/AP hide caption

itoggle caption Fareed Khan/AP