If I was paranoid, I would notice that we invaded Afgghanistan only two years after they had completely eliminated poppy growing. The taliban edict against growing poppies was the most effective anti-drug measure ever, and it caused thier stockpiles to become immensely valuable.

Once the money dried up the US may have become agitated and looked for the first exuse they could find to remove the taliban and resume the flow of opiates.

Very much like what happened in Iraq with the oil.