This paper seeks to provide a general template for determining the nature of, and reasons behind, the employment of women in warfare. I focus on groups of women who fought as formal combat components of historical military forces in order to explain the general socio-cultural, military, and situational factors that led to the employment of women in combat. My conclusions are that two factors: societal license to fight and the presence of battlefield roles with able women to fill them, were necessary for the regular employment of women in combat. However, I also found that under desperate circumstances in existential conflicts, societies, regardless of their disposition towards women or traditional battlefield roles, would employ women in combat to stave off destruction. My sources are drawn from a wide variety of historical records of women in combat, including writings of Plutarch and Appian, and modern analyses of archeological findings that suggest martial roles for women. The scope of this paper is from the 6th Century BCE to 1900 CE.