The military has gang problems simply because it's a microcosm of the surrounding society…. While military background checks aim to root out candidates who have a history of criminal gang activity, they don't find those who have never been caught.
This observation is consistent with my experience, that except for pacifists, you generally see a cross-section of society represented in the military. And just as society has not eliminated gangs or extremists, neither can the military. So while human nature makes it impossible to eliminate all misconduct, one nonetheless hopes the military could root out an organized criminal element before training its members to be more efficient killers.
According to citations found in this 2009 Yale Law Journal article, it appears CID has been drafting yearly reports on the military’s gang problem since at least 2006. Multiple sources have noted the military’s gang problem over the last 15 years, with many reporting increased gang activity and extremist views year-over-year. Whether this is a result of the data being tracked more systematically or of noteworthy examples of anecdata breaking through in the news, this is nonetheless an alarming issue. So to the extent the uptick is real, is it a response to the failings of the military, of our society, or both?
As for another piece of anecdata, the Guardian reminds us that white supremacists have used the military as a training ground to commit terror before—Timothy McVeigh was a white supremacist and decorated Gulf War veteran after all. So considering how long we’ve been dealing with this, are civilian leaders and the military adequately addressing this problem?