Suicide - not combat - is the leading killer of U.S. troops deployed to the Middle East to fight Islamic State militants, according to newly released Pentagon statistics. U.S. casualties have been relatively low since the U.S.-led war effort began with a bombing campaign in August 2014, reflecting the limited combat exposure for troops. Of the 31 troops who have died as of Dec. 27 in Operation Inherent Resolve, 11 have taken their own lives. Eight died in combat, seven in accidents and four succumbed to illness or injury. The cause of one death is under investigation. The reasons suicide ranks as the No. 1 cause of troop deaths ... likely include mental illnesses that enlistees brought with them to boot camp, post-traumatic stress, multiple combat deployments and heightened anxiety in a military at war for 16 years. By far, 2016 has been the most dangerous for U.S. forces since the war began. Seven of the eight combat deaths have occurred in 2016, and 21 of the 26 troops wounded in action suffered their injuries this year. But the military's suicide problem continues. Between 2001 and 2010, the rate of suicide in the military doubled. The chief spike occurred around 2005 when fighting and combat deaths soared in Iraq and Afghanistan, and the Army shouldered most of the wars burden. The Army still has the highest percentage among the services for suicide. As a whole, the militarys rate of suicide of about 20 per 100,000 troops in 2014 was comparable to the same civilian population.