I'm going to say TRUE ... although it would help to have more specific context on the span of history your question covers when it says, "historically speaking." And by "US army casualties," I wonder if the question means only the Army and not Navy, Air Force or other branches of service.
Let's look at the overall picture. As reported by the New York Times in 2003, upt that point in the history of the US at war, over 650,000 Americans were killed in combat. Another 243,000 died during the time that wars were being fought, but from training accidents, injury or disease.
The accident rate of deaths for US military personnel seems overall higher in recent years. As reported by the Armed Forces Health Surveillance Center, from 2004 to 2007, deaths caused by war-related injuries accounted for 40% of all deaths of military personnel. Traffic accidents, other accidents, and suicide accounted for the other deaths. (Suicides accounted for 20% of military personnel during that period of statistical measurement.)