Next week the United Nations is convening the largest gathering on drug policy that the world has seen in two decades. It was the brainchild of three Latin American presidents — from Colombia, Guatemala and Mexico — who wanted to end decades of poorly conceived and executed counter-narcotics programs. Their hope was that the General Assembly Special Session, or UNGASS, would stimulate new thinking on ways to reverse the political, social and economic wreckage of a failed war on drugs.