When Women Were Warriors is not set in an alternate timeline or a fantasy universe, because that would imply that women can be the equals of men only in a world that doesn’t really exist.
Significant evidence suggests that, during the Neolithic age in northern Europe and probably elsewhere, matrifocal societies flourished in which women were the owners of productive land, the heads of households, and the leaders of their communities. There is certainly documented evidence from Roman times of female warriors among the Celtic tribes, and the tradition of inheritance through the female line was practiced by both the Celts and the Picts and persisted well into the historical period.
When Women Were Warriors is set in the early Bronze Age, which may be a bit late historically for a matrifocal society, but so many of our archetypal symbols come from post-Stone Age technology that strict historical accuracy must yield to mythical authenticity. Swords resonate with most of us in a way that stone axes do not.
When Women Were Warriors is about people who could have lived in a place we would recognize in a time that our questing selves remember. And it is just as much about people who may someday live in a place we would find familiar in a time we are beginning to imagine.