Smack in the Middle

ALEXANDRA BOULAT/VII

Pakistani addicts gather to smoke heroin under a bridge in Quetta

Kandahar, the citadel of Taliban rule, has its own version of Wall Street called the opium bazaar, just beyond the stalls selling raisins and pistachios. And the Taliban is guilty of insider trading. Two summers ago, some of the biggest customers in the clamorous lane were local Taliban commanders who had been tipped off that the supply was about to be choked—Taliban supreme leader Mullah Mohammed Omar declared poppy cultivation to be "un-Islamic"—and saw the chance to make a killing.

[an error occurred while processing this directive]Back then, it was a bearish market. Afghanistan provided 75% of the world's opium and its...