Statistics on Afghanistan tend to favour either the financial drain or the dead and seriously wounded. Yet the raging decade long conflict between insurgent, puppet Karzai government and ISAF counterinsurgency forces have created a vast number of displaced people. The Internal Displacement Monitoring Centre gives a damning verdict (.pdf here):
"The UN and ICRC have recorded that 730,000 people have been internally displaced in Afghanistan due to conflict since 2006, an average of 400 a day. At the end of January 2011, 309,000 people remained internally displaced due to armed conflict, human rights abuses and other generalised violence. This figure was higher than at any time since 2005.
While armed opposition groups have been responsible for the majority of killings, most of the documented mass displacements have occurred as a result of offensives by international forces."
Perhaps most of the documented mass displacements are a result of offensive by ISAF forces because they document these displacements for more thoroughly or perhaps because it's easier to cite foreign intervention rather than Taliban generated displacement. But most likely, the escalation of bombing to win has created uninhabitable settlements. Look here at a Paula Broadwell blog post on airpower.
Recent drought in Afghanistan has similarly led to migration. We tend to think of Afghanistan as a "security situation" but drought in northern, north-eastern and western provinces of Afghanistan means that three million (of the twenty two million population still inside Afghanistan's borders) face severe food shortages. Insecurity means that aid to the afflicted regions is extremely difficult:
But in the face of continuing conflict, it becomes difficult to effectively operate, say observers in Kabul. “Billions of dollars have been sunk into Afghanistan in search of durable long-term solutions, but until the security question is solved, little can be achieved,” an international aid worker told IRIN.
A Food Security Risk Index of 196 countries released on 31 August by Maplecroft, rates Afghanistan number nine. It says the country faces extreme food insecurity and that a major driver of this is conflict and displacement.