For nine months in Kandahar, Afghanistan, I went through the same routine every day.

I put on my uniform and tied my boots. I put a magazine in my 9-millimeter handgun and locked it in my hip holster. I put a 30-round magazine in my M4 and slung it over my shoulder. If the day included a patrol, I put on my body armor. I usually carried a knife and at least one tourniquet. Every day, our team discussed base security to identify where we were most prone to attack.

That was my standard procedure while serving with the United States Army in a combat zone. When I left active duty in 2014, I never...