It's all about natural resources, especially oil, new markets to flood with american products. It's kind of funny to think that the reason of wars are still religion related. It's not like the palestinian/ israel conflict is based upon religion anyway. It's not like America started a war in Afghanistan to bring democracy or school the little kids so they can be free kids or whatever bullshit. It's all about interest and making a reason, that follow their principles of justice, equality and shit to justify the intervention in front of the public opinion.
Guys just read a bit about history, just for opium many wars started. Afghanistan war could be no different. War on drugs bullshit... When Taliban took control over most lands in afghanistan, in 2001 with the leader Mohammad Omar, opium production fell from 3330 tons to 200 tons a year because he believed it was harmful. After a few month, America entered the war and again opium production rised. Coincidence?