The idea that men are aggressive while women are coy and nurturing "by nature" cannot stand up to closer scrutiny. For instance, female rulers and warriors have always existed. Unfortunately, there is only one well-documented example of a society where a substantial portion of the troops were women: the West African kingdom of Dahomey during the 17th, 18th and 19th centuries. Stanley Alpern's book "Amazons of Black Sparta" tells the story.
The territory of Dahomey comprised a large part of southern Benin, including the towns of Allada and Whydah. The dominant ethnic group were the Fon, who at this time still practised their traditional religion, although Christian missionaries sometimes visited the kingdom. What made Dahomey stand out was the presence of female warriors in their army. At most, they numbered around 6000. Western visitors called them Amazons, and during the 19th century, even the Fon themselves began to refer to their female warriors in this manner. The Amazons had to be celibate, lived in the royal palace complex, and were a privileged elite within Dahomean society. When not fighting, they earned a living by pottery or embroidery. Some hunted elephants. The Amazons were definitely used in military combat, so their status wasn't simply symbolic.
Alpern points out that Dahomey wasn't a particularly pleasant society. Actually, the kingdom was deeply implicated in the transatlantic slave trade, carrying out slave raids on defenceless villages, and selling the captives to the European slave-traders for a profit. Captives from the interminable wars with other kingdoms met the same fate - if they were lucky. The Fon practiced human sacrifice! The entire kingdom was militarized and ruled in top down fashion by the royal family. One European visitor dubbed it "Black Sparta". Exactly why Dahomey, but not other West African kingdoms, employed women warriors, is unknown. Large losses of male warriors during the constant wars might have been one factor, and since the population of Dahomey was relatively small, recruiting women became a logical option.
Alpern claims that Dahomey was patriarchal, despite the Amazons. However, other descriptions of this peculiar kingdom call its gender structure "dualist". According to Dahomean religion, every male office had to have a female counterpart, and the presence of both male and female warriors in the royal palace complex might be explained by this. Alpern admits that it was sometimes possible to influence the king by petitioning the queen through one of the Amazons, but he doesn't explore this further, although he mentions the dualism several times. Alpern's notion that Dahomey was obviously patriarchal is the main weakness of the book - as if traditional patriarchy is the only alternative to modern notions of gender equality.
Otherwise, "Amazons of Black Sparta" is a well-researched book, often based on rather obscure sources. All aspects of Amazon life are covered: recruitment, training, actual battles, and the eventual downfall of Dahomey in 1892 at the hands of the French. Indeed, the book is so detailed that it often gets hard to read! Still, I give it fours stars. If a militarist society like the one in Dahomey could include thousands of women in its armed forces, there might as well have been other societies of this kind. It's a pity they have been lost to history.