Which of the following is NOT a historical factor for suicide identified in the Army?

The correct answer is social isolation. While social isolation can indeed be a contributing factor to suicidal thoughts and behaviors, it is not categorized as a historical risk factor in the Army's definitions and studies related to suicide. Historical factors typically include known risk indicators that have a strong correlation with a higher likelihood of suicide in individuals.

Alcohol or drug abuse is a well-documented historical factor as it can lead to decreased judgment, increased impulsivity, and a greater propensity for suicidal behavior. Similarly, a previous attempt of suicide is one of the strongest predictors of future attempts, thereby placing it firmly within the historical risk factors. The suicide of a friend or family member also falls into this category because it can significantly impact individual mental health and increase the risk of suicidal ideation and behavior.

Social isolation, while an important aspect of mental health that can exacerbate suicidal feelings, does not serve as a historical factor in the same manner, making it the correct choice for this question.