The images of the Boston bombing reminded me of things I saw in southern Helmand province, not the streets where I usually do my Christmas shopping. Many witnesses described the marathon carnage as “a war zone,” and indeed it was: mangled flesh, shocked faces, splattered blood. …

I deployed to Afghanistan believing my presence in that country would help stop attacks such as Boston’s from happening. But instead, my war has spilled over, striking the city where my 22-year-old brother goes to school and where my mom, until recently, felt perfectly safe eating lunch outdoors. …

It wasn’t always easy to justify serving in a war that has devolved from its initial aim of ousting the Taliban and al-Qaeda to a nation-building effort that appeared to have come 10 years too late. The conflict has dragged on for more than a decade, becoming increasingly unpopular after years of mixed results and no clear definition of victory. The counterinsurgency mantra of “clear-hold-build” echoed in our ears as we fought an elusive enemy and slowly pushed them out of the city centers. Day by day, we measured victory by the number of wells we helped build and the time that passed without a casualty. …

While I was deployed, I went to bed at night believing that I was protecting the homeland because coming after me and my fellow Marines was a much easier commute for those so hell-bent on killing Americans. But that argument no longer makes sense if my war has inspired enemies at home.