Without the foreign troops, Afghanistan would be partitioned, and embroiled in a civil war between the Pushtun tribes, with the non-Pushtun tribes standing aside, or taking part, as their own internal politics dictated. All this would be paid for by the sale of heroin. That would irritate Afghanistan's neighbors (particularly Iran and Pakistan, which already have a serious drug addiction problem), as well as the rest of the world. You either take care of it now, or deal with it later. stop pissing on people who risk their lives to deal with a situation.