Yesterday, October officially became the deadliest month for U.S. forces in Afghanistan since the war began. The death toll was pushed over that grim marker by improvised explosive devices (IEDs), the single deadliest weapon used against U.S. forces in Afghanistan. IED deaths have increased alongside U.S. troop increases every year since the U.S. invaded.

Paraphrasing Joint IED Defeat Organization Director Lt. Gen. Thomas Metz, Stars and Stripes reported today that:

IED attacks in Afghanistan have gone up along with the rising troop levels and likely will continue to increase if more U.S. forces are sent there…

That’s a real problem for the measure of success set out by General Stanley McChrystal for the U.S. effort in Afghanistan:

American success in Afghanistan should be measured by “the number of Afghans shielded from violence,” not the number of enemy fighters killed, he said.

What’s the connection? Well, it turns out IEDs are also the single greatest conflict-related killer of civilians. The fact that the use of IEDs increases along with U.S. troop deployments explains the similarity between these two graphs:

Civilian Deaths Compared to Troop Deployments

Military officials have warned that sending more troops to Afghanistan will likely result in a “tough fight” (read: rising U.S. casualty rates). If President Obama adds more troops in Afghanistan, especially in densely populated areas, get ready to see another major spike in civilian deaths as well.

Note: Derrick Crowe is the Afghanistan blog fellow for Brave New Foundation / The Seminal. Learn how the war in Afghanistan undermines U.S. security: watch Rethink Afghanistan (Part Six), & visit http://rethinkafghanistan.com/blog.