I'm not a history buff but I don't think female leaders in the past have shied away from war. I don't really think women are less inclined towards conflict, but theres the physical aspect which can be intimidating in a woman-man scenario, and the cultural aspect with either woman-man or woman-woman. In a all women world neither of these would have much effect.
Perhaps a good model for the society, and especially government, would be a women-dominated profession, or maybe a all girls school. Probably not that much different.
Personally I think the differences between men and women are variations on a theme, rather than yin and yang, mars and venus.
(Interestingly I read in an old National Geographic that for ancient South Americans Venus was the god of war.)